Your Buddy session automatically terminates every half hour, effectively the same as logging into BuddyAuth and killing your session. The only difference is that PF can automatically log you back in when this happens, which it does.
If someone doesn't know how to use BuddyAuth or something and can't kill their session it's done automatically every half hour or so so they don't get stuck with a session that's forever active. If PF is actually closed and doesn't renew the session when it's automatically killed then it stays killed and they can log back in.
Hanging on that message isn't normal, but the session expiring isn't a bug. It's the same as the site for your bank or school logging you out after being inactive for a while, it's a security measure that's perfectly normal.