There's actually 2 logins, your forum one, and your RA one.
If you're getting the login prompt on the menubar, but NOT the forums, then it's actually working fine. (RA accounts currently have no longterm option, I'm going to fix this on next release.)
If it IS actually logging you out of the forums, then you likely have cookies turned off, or you didn't use the same browser.
If none of these are the case, let me know... but it's been holding my forum login fine.