I think we ALL hate powers of attorney!
If A and B jointly own an account, A can appoint B his/her attorney in fact, and the bank can act on the POA without problem. Often, a bank includes special POA language in its account agreement to cover just such challenges.
The reverse is not true. That is, if A is attorney in fact for B, A cannot -- in most states and in most cases -- create joint ownership of B's account for himself (or anyone else).
(Edited to correct an error pointed out by "Anonymous" in post that follows -- JSB)
John S. Burnett
Fighting for Compliance since 1976
Bankers' Threads User #8