So this is probably lame advise (but that happens to me some times and the only way(s) that it changes is when I either refresh or in most cases
log out and delete cookies, temps, and history and then log back in.
Its a pain but...ehhh I am almost just used to it now

.
A good example for me would be when I accidently hit reply or qoute before I log in. And I get the you need to sign in thingy... well even if I sign in I am doomed to it not working unless I do all of the listed above^^^.
so I hope that helps
otherwise I just really hope its a little glitch.