Hi Erwin,
Thanks for the suggestion. The *REALLY* weird part about this is that I'm using the vbulletin URL's to test this out--it DOESN'T happen when I use the rewrite urls. (i.e.
http://www.domain.com/forums/index.php?s=######...)
I don't want to force them to use cookies though

... I'm staring at the apache rewrite rule manual now trying to figure out what I'm missing here.