Title says it all. I think it's something that's been overlooked. One stole my Draconic Bow, and when I killed it, it didn't drop it. I turned mobGriefing off and keepInventory on for a reason...

Will be fixed; babies don't steal if you wear an Enderman Head, but they always drop the item they hold. If you also turn off mob drops, it might not work though.

I didn't know that about wearing the heads. Mob drops is on. I figured it would drop it when it died, but I tore apart the surrounding landscape with a magnet, and didn't get my bow back, so I don't know what happened.

Any mod that can modify mob drops?

I have no idea. I can post all the mods I have installed if it'll help. It's basically FTB Infinity with extras.

Not really, I don't know which mods could cause it.