The derailleur isn't implicated in anything that happens when backpedaling foe the simple reason that it isn't there.

The chain is coming unguided to the rear sprocket, so anything can cause it to hop in either direction. If you lean the bike up and backpedal in a combination where this happens, odd are you'll note that the chain brushes the next sprocket very slightly, and it wouldn't take much for one of the teeth to snag and lift it, especially because they're designed do precisely that.

This is lie the old joke where someone tells the doctor, "my arm hurts whenever I lift it like this..," and your answer is the same as the punch line.

BTW - you didn't say, but your problem is more common with newer chains and sprockets. With some wear the edges dull and they are less prone to snagging and shifting.