Goran,
I had a major formatting mess in 4.1.3 w/ Thickbox...
http://forum.x-cart.com/showthread.php?p=140060
Basically, enabling the Thickbox incude destroys my <p> tags in the "detailed product decriptions" - and causes the pulldown qty box to shrink (horizontally).
I am going to look into the CSS and see what's going on...
Disabling {include file="thickbox/thickbox_include.tpl" } restores the formatting.
I am sad. I was L-O-V-I-N-G this mod. Let's see if I can find something...