Cardboard boxing (storing a block in a cardboard box) the top half or bottom half of a standard Minecraft door places the cardboard box in the world. The other half of the door disappears.

Breaking the block will yield the item.

Hovering over the item in your inventory (or another, such as that of a chest) causes the entire client to crash with the following error. I assume this happens because door halves do not have a name associated with them, so the NullPointerException is thrown when nothing is returned [Just my guess].

java.lang.NullPointerException: Rendering screen
at net.minecraft.item.ItemStack.func_82833_r(ItemStack.java:507)
at mekanism.common.item.ItemBlockCardboardBox.func_77624_a(ItemBlockCardboardBox.java:55)
at net.minecraft.item.ItemStack.func_82840_a(ItemStack.java:614)
at net.minecraft.client.gui.GuiScreen.func_146285_a(GuiScreen.java:136)
at net.minecraft.client.gui.inventory.GuiContainer.func_73863_a(GuiContainer.java:166)
at net.minecraft.client.renderer.InventoryEffectRenderer.func_73863_a(InventoryEffectRenderer.java:51)
at net.minecraft.client.gui.inventory.GuiInventory.func_73863_a(SourceFile:47)
at net.minecraftforge.client.ForgeHooksClient.drawScreen(ForgeHooksClient.java:382)
at net.minecraft.client.renderer.EntityRenderer.func_181560_a(EntityRenderer.java:1094)
at net.minecraft.client.Minecraft.func_71411_J(Minecraft.java:1076)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:371)
at net.minecraft.client.main.Main.main(SourceFile:124)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

You can view the full log, including my mods and system details here, though I don't deem them useful: http://paste.ie/view/973ac411