Emachine9643: Had the same problem I guess I had too many programs that stored cookies (firefox, ccleaner, etc) so I once I deleted the ones in ccleaner (i think) it cleared it up.
CCleaner just removes trash like cookies and so on and does not store or create cookies ;-) It will delete the cookies of your browser if you set this option.
DanielRuf: this wouldalso delete / invalidate your cookies so this is just a cookie (and possibly cache) problem ;-)
Goodaltgamer: Yep, and no need to delete all of them what a few guys have suggested ;)
Cache seems not to be involved, as I only logged out and in again. So something to do with one of the cookies, but was to lazy to check for it. Only funny didn´t had the problem prior, only after changing my password it did happen.
Did not check this but I regularly clean my PC from cookies and so on as they aremostlynot needed ;-) =)
Might be the case that there is a new cookie created when you change your password which forces you to relogin but this cookie is not invalidated / deleted properly.
It is a feature, not a bug ;-)