Problem, minor, PR comes with backpacks
Result, SEVERE, savegame corruption

Crash Report posted here:
http://www.minecraftforum.net/topic/1885652-164forge-multipart-projectred-v43431-412014/page__st__2660#entry30259582

I have used the backpacks mod for some time and have put off using Project Red backpacks cause they seem glitchy... Putting items in them can take 5 clicks. Maybe that's deliberate since it seems to be the way with many PR inventories...

It appears that the OreDictionary.oreStacks HashMap was changed at some point during iteration. Which only could happen if another thread calls OreDictionary.getOres(Integer id) or getOreID(String name) but I think that is unlikely, or is it?

Don't know, but can guarantee that a backpack can't corrupt a save.