I had several AP's and clients that I upgraded to V5rc4 for testing that I had to downgrade back to 4x because of issues I mentioned below. Clients would randomly "lock" up as in they would still show in the registration list on the AP but you couldn't pass any data to the clients. No ping, mac ping, mac telnet, nothing. If you disable the AP interface the clients would start passing data again for a random amount of time before they lock up again. If you look at the log on the client radio it shows the disconnect error messages that I listed but the AP log never shows the clients as disconnecting.
Anyway V5 seems to be far from stable, even for testing purposes.