The preg_replace in theme/yui_combo.php does not take into account images that have numbers in their name. Example image: lib/yui/2.8.2/build/treeview/assets/skins/sam/treeview.css there are images check0.gif, check1.gif, check2.gif.
The way I fixed it was to look for trailing numbers, but I don't think this is the best solution. Example:
But that didn't seem to work.