Do you have any unusual cookie/session settings in vB? That being shorter than usual timeout, things like that.
For some reason the session has expired when you switch back to Oblivion Knight. I'll look into this for 1.1.1 or 1.2 *nods*
If it can be fixed, which I believe it can, then it's likely not going to be a drastic change to the code I introduced in login.php.