I recently came across an IE7 only bug that I thought I'd share so when I come to this site 6 months from now to figure out the same thing, I'll have it on hand.
I believe the easiest way to recreate this bug would be the following:
<div style="overflow: auto; height: 150px;">
<div style="position: relative;">[...]</div>
</div>
In IE7, the outer div is a fixed size and the inner div is relatively positioned and contains more content (assuming the inner div causes an overflow). In all other browsers, this seems to work as expected.