[TECK]

Elem, set the $bburl (vBulletin forum URL) to a normal URL type. (best way)

OR

Try setting in each file (above [high]eval( 'dooutput[/high]) and each function (below [high]function archive...[/high]) this code:
$cleanurl = 'http://www.yoursite.com/forum';

where the clean URL listed above is the un-redirected one.

Then replace in all script files and templates [high]$bburl[/high] with [high]$cleanurl[/high]

I don't offer support for this issue, so hack it at your own risk, since I will never use this type of redirection who creates only problems with cookies and many other issues.