Of course it would be silly. That's my point: If everybody duplicated their threads we would in practice have just one big forum, since all the the threads would be duplicated in every forum.
See above. Or choose more carefully. But choose.
I can think of a couple of reasons for this: Either noone knows. Or, more importantly, they can't be bothered because of post #3.
Anyway, I would put it down to a bug - either in the OS or the apps themselves. I take it you tried restoring the phone itself? It's not as if there are many options when it comes to fault finding on the iPhone.