I set up several Miner and Picker robots in a cave, and waited until they all came back to their stations for good. After surveying the cave, I found the following ores NOT mined:

-Yellorite (Big Reactors)
-Osmium (Mekanism)
-All Infused Stone (Thaumcraft)

I have Buildcraft-Compat installed, and insured the blocks were within the robots' radius. Oddly enough, the following ores WERE mined:

-Tin and Copper (Mekanism)
-Amber and Cinnabar (Thaumcraft)

If this is a repeat issue, I apologize, similarly if I'm barking up the wrong tree. Absolutely fabulous mod, can't wait to see what's added/updated for 1.8.9. :D

Edit 1: Miners were using vanilla Diamond Pickaxes

Edit 2: Have reached out to respective developers.

mekanism/Mekanism#3078
erogenousbeef-zz/BigReactors#559
(Erogenous Beef has disappeared from modding, at least for a while. This is the issue posted to the maintainer's github: Tomson124/BigReactors#1)
Azanor/thaumcraft-5#323 (Azanor has upgraded the things on his end.)

Sorry, I forgot to ask: Is this 1.8.9 or 1.7.10? I assumed 1.7.10 but I might be wrong...

Oops!

1.7.10. Thaumcraft is the only mod available to the general public for 1.8.9, of those involved.

[taps foot, updates OP]

Edit: BC 1.8.9 is in alpha, see below.

Thanks :)
EDIT: BC is public for 1.8.9 as well, but I guess you didn't include it in the list of "involved mods"

Maybe I'm just being stupid, but I don't see it.

http://www.curse.com/mc-mods/minecraft/buildcraft#t1:other-downloads
http://minecraft.curseforge.com/projects/buildcraft/files

I don't doubt you, I just can't find it anywhere. Where have all these new mods been uploaded? D=

Sorry, I've kept the releases away from curse and the official BC website because its in alpha, so I've been pushing them to the forums (http://www.mod-buildcraft.com/forums/showthread.php?tid=1853&pid=18186#pid18186)

Oh wow. That makes sense. Color me very pleasantly surprised. =D

Sorry for not responding to this when I first saw it, I assume the not-mining is due to the way the blocks in the mods works- but I'll look into this a little bit to see if it really is a buildcraft issue.

EDIT: I don't know how Mekanism is meant to be played (or how two of the three blocks break but the others don't) so this behaviour may be intentional. Same with Thaumcraft, although I can't see its source to check.

The miner robot can dig any block whose oredict name starts with "ore": https://github.com/BuildCraft/BuildCraft/blob/7.2.x/common/buildcraft/core/properties/WorldPropertyIsOre.java#L27 . It's probable that those ores have a naming scheme that doesn't match this expectation.

Hmm, okay. Should I go poke Azanor, Erogenous Beef, and Aidan?

Thanks @hea3ven, however according to https://github.com/aidancbrady/Mekanism/blob/master/src/main/java/mekanism/common/Mekanism.java#L926-L928 all 3 start with "ore" so I assume the issue is todo with something more than just that.

Asking the other mod authors might be a good idea :) (In a worst case scenario we might need to add a "white-list" or something similar to allow for any custom ores to register themselves (for example from BC|Compat)

Isn't there ways for mods to tell each other through an API what kind of requirements there are for breaking a block? Can a robot with a wooden pick break Iron Ore?

Oh, oops! I should've mentioned: All Miners were given vanilla diamond pickaxes.

Updated the OP with this info, and provided links to the other reports.

Just having the requirement to be able to break a block isn't enough unfortunately, as cobblestone can be broken with just a wooden pick, but we don't want a miner to break it. (and other mods add blocks that are as common as cobblestone so we can't just blacklist stone)

And, we're just waiting on Mekanism and Big Reactors.

As erogenousbeef seems to quit modding (at least for now), me and probably some other guys will maintain BigReactors. I recently updated it and all dependencies it had including Buildcraft, but I didn't tried it yet if that did the thing... Maybe you could do so and post me an issue on my Github repo if it is still not working.
https://github.com/Tomson124/BigReactors/releases

I have tested it, and it does not fix the issue. But thanks for the response and the dev update, glad I could help.

Not our issue.