(Overworld)
Despite being able to do so in creative (server), I can't pick up lava, even momentarily, in a wooden bucket while in survival. I tried right click, shift right click, left click, and shift left click in survival. When I tried the last (shift left click) in survival in single player, it actually crashed the client. (log below).

When in creative on the server, I was able to pick up the lava briefly (destroyed bucket) in order to move the source block out of the barrel and onto the ground for further use. This, of course, in survival would require life sacrifice, but hey, that's the only way I could figure out how to get the lava into place and out of the barrel. Is this the intended method of getting the lava out til you get an iron bucket, or did I miss some blindly obvious way to get it out? :P (Note: I tried breaking the barrel on the server (without lid) to see if it would spill out, but it didn't.

I ended up giving myself a lava source block after spending some time attempting to get lava out of the stone barrel via wooden bucket in survival and failing. I did use the wooden bucket method (plus life sacrifice) in order to move it one block over to the 'official' spot for my cobble gen. ;)

Single player CRASH LOG

---- Minecraft Crash Report ----
// Don't do that.

Time: 26/06/15 10:26 PM
Description: Ticking memory connection

java.lang.NullPointerException: Ticking memory connection
at subsistence.common.block.machine.BlockBarrel.func_149699_a(BlockBarrel.java:141)
at net.minecraft.server.management.ItemInWorldManager.func_73074_a(ItemInWorldManager.java:165)
at net.minecraft.network.NetHandlerPlayServer.func_147345_a(NetHandlerPlayServer.java:489)
at net.minecraft.network.play.client.C07PacketPlayerDigging.func_148833_a(SourceFile:53)
at net.minecraft.network.play.client.C07PacketPlayerDigging.func_148833_a(SourceFile:8)
at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:212)
at net.minecraft.network.NetworkSystem.func_151269_c(NetworkSystem.java:165)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:659)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:547)
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:111)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:427)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685)

A detailed walkthrough of the error, its code path and all known details is as follows:

-- Head --
Stacktrace:
at subsistence.common.block.machine.BlockBarrel.func_149699_a(BlockBarrel.java:141)
at net.minecraft.server.management.ItemInWorldManager.func_73074_a(ItemInWorldManager.java:165)
at net.minecraft.network.NetHandlerPlayServer.func_147345_a(NetHandlerPlayServer.java:489)
at net.minecraft.network.play.client.C07PacketPlayerDigging.func_148833_a(SourceFile:53)
at net.minecraft.network.play.client.C07PacketPlayerDigging.func_148833_a(SourceFile:8)
at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:212)

-- Ticking connection --
Details:
Connection: net.minecraft.network.NetworkManager@791f3da0
Stacktrace:
at net.minecraft.network.NetworkSystem.func_151269_c(NetworkSystem.java:165)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:659)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:547)
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:111)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:427)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685)

-- System Details --
Details:
Minecraft Version: 1.7.10
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.8.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 872158344 bytes (831 MB) / 1928331264 bytes (1839 MB) up to 3817865216 bytes (3641 MB)
JVM Flags: 4 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx4096m -Xms256m -XX:PermSize=256m
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP v9.05 FML v7.10.113.1384 Minecraft Forge 10.13.3.1384 75 mods loaded, 75 mods active
mcp{9.05} Minecraft Coder Pack Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
FML{7.10.113.1384} Forge Mod Loader Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Forge{10.13.3.1384} Minecraft Forge Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
appliedenergistics2-core{rv2-stable-3} AppliedEnergistics2 Core Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Aroma1997Core{1.0.2.13} Aroma1997Core Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
CodeChickenCore{1.0.4.35} CodeChicken Core Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
NotEnoughItems{1.0.4.95} Not Enough Items Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
TubesCore{${version}} Tubes Core Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
bspkrsCore{6.15} bspkrsCore Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
ArmorStatusHUD{1.28} ArmorStatusHUD Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
IC2{2.2.706-experimental} IndustrialCraft 2 Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
AdvancedMachines{1.1.3} IC2 Advanced Machines Addon Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
AdvancedSolarPanel{1.7.10-3.5.1} Advanced Solar Panels Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
appliedenergistics2{rv2-stable-3} Applied Energistics 2 Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Aroma1997CoreHelper{1.0.2.13} Aroma1997Core|Helper Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
AromaBackup{0.0.0.5} AromaBackup Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
bedrockium{1.0.0} Bedrockium Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
BiomesOPlenty{2.1.0} Biomes O' Plenty Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
BuildCraft|Core{7.0.11} BuildCraft Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
BuildCraft|Energy{7.0.11} BC Energy Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
BuildCraft|Factory{7.0.11} BC Factory Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
BuildCraft|Robotics{7.0.11} BC Robotics Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
BuildCraft|Silicon{7.0.11} BC Silicon Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
BuildCraft|Transport{7.0.11} BC Transport Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
BuildCraft|Builders{7.0.11} BC Builders Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Forestry{3.5.7.16} Forestry for Minecraft Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
BuildCraft|Compat{7.0.8} BuildCraft Compat Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
CarpentersBlocks{3.3.5} [Carpenter's Blocks](Carpenter's Blocks v3.3.5 - MC 1.7.10.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
ForgeMultipart{1.1.2.331} Forge Multipart Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Baubles{1.0.1.10} Baubles Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Thaumcraft{4.2.3.5} Thaumcraft Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
chisel{2.3.10.37} [Chisel 2](Chisel 2 - 2.3.10.37.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
CustomMainMenu{1.3} Custom Main Menu Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
ttCore{MC1.7.10-0.1.0-66} ttCore Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
customthings{MC1.7.10-0.0.2-29} CustomThings Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
EnderIO{1.7.10-2.3.0.378_beta} [Ender IO](EnderIO - 2.3.0.378 - Beta.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
extracells{2.2.71} Extra Cells 2 Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
ExtraUtilities{1.2.2} Extra Utilities Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
McMultipart{1.1.2.331} Minecraft Multipart Plugin Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
GardenCore{1.7.10-1.6.2} Garden Core Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
GardenContainers{1.7.10-1.6.2} Garden Containers Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
GardenStuff{1.7.10-1.6.2} Garden Stuff Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
GardenTrees{1.7.10-1.6.2} Garden Trees Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
GraviSuite{1.7.10-2.0.3} Graviation Suite Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
HardcoreDarkness{1.5} Hardcore Darkness Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
hardcoremapreset{1.2.1} HardcoreMapReset Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
HelpFixer{1.0.7} HelpFixer Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
HopperDuctMod{1.3.2} Hopper Ducts Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
HardcoreQuesting{The Journey (4.2.4)} [Hardcore Questing Mode](HQM-The Journey %284.2.4%29.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
infernalskycolor{0.8} Infernal Sky Color Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
inpure|core{1.7.10R1.0.0B9} INpureCore Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
inventorytweaks{1.59-dev-152-cf6e263} Inventory Tweaks Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
IronChest{6.0.62.742} Iron Chest Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
launchgui{1.7.10-2.0-14} LaunchGUI Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
LoreExp{1.0.5} Lore Expansion Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
MineTweaker3{3.0.9B} MineTweaker 3 Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
modelcitizens{1.0.1} Model Citizens Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
modpackTweaks{1.2.0} [ModpackTweaks](ModpackTweaks - 1.2.0 CUSTOM.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
modtweaker2{0.8.2} [Mod Tweaker 2](ModTweaker 2-0.8.1.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
MouseTweaks{2.4.4} Mouse Tweaks Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
nmsot{1.0.0} No Mob Spawning on Trees Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
harvestcraft{1.7.10g} [Pam's HarvestCraft](Pam's HarvestCraft 1.7.10h.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
PowerConverters{1.7.10_3.2.2-jenkins.70} Power Converters Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Progression{0.4.0} Progression Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
RIO{2.3} RemoteIO Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
ResourceLoader{1.0} Resource Loader Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
sprinkles_for_vanilla{1.2.9} sprinkles_for_vanilla Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
subsistence{Alpha} Subsistence Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
td{@Version@} TeleDimension Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
thaumcraftneiplugin{1.7.10-1.6a} Thaumcraft NEI Plugin Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
TooMuchTime{2.4.0} TooMuchTime Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
tpv-command{0.0.2.00} Teleport Command Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
trophyslots{1.2.5} [Trophy Slots](Trophy Slots-1.7.10-1.2.5-universal.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Tubes{2.0.5} Tubes Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
ForgeMicroblock{1.1.2.331} Forge Microblocks Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
AE2 Version: stable rv2-stable-3 for Forge 10.13.2.1291
AE2 Integration: IC2:ON, RotaryCraft:OFF, RC:OFF, BC:OFF, RF:ON, RFItem:ON, MFR:OFF, DSU:ON, FZ:OFF, FMP:ON, RB:OFF, CLApi:OFF, Waila:OFF, InvTweaks:ON, NEI:ON, CraftGuide:OFF, Mekanism:OFF, ImmibisMicroblocks:OFF, BetterStorage:OFF
Profiler Position: N/A (disabled)
Vec3 Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Player Count: 1 / 8; [EntityPlayerMP['ValsNoisyToys'/9, l='Infernal Skies', x=4.30, y=64.00, z=4999.48]]
Type: Integrated Server (map_client.txt)
Is Modded: Definitely; Client brand changed to 'fml,forge'

Reported on the Subsistence repo.