I've heard various moans about the new iOS concerning this type of thing. I'm still on a prehistoric version, and have no problem with retaining my Mudcat log-in, so I imagine it's to do with the upgrade.

Probably if you go on one of Apple's iPad forums to have a good moan about it you'll find a lot of others already moaning in chorus. Their techies tend to pay attention to those discussions, and often even answer questions, so that's probably the best way to get them to issue a fix, or else tell you what to do.

Let us know via this thread how you get on. Meanwhile I'll stay in my nice warm iOS4 cave till it's safe to come out.
#ifitaintbrokedontfixit