Movie set thumbs/fanart coming up empty?

When I update XBMC setting to use "Group Movies in Sets" on Mac, it correctly selects a fanart and a thumb to represent the "collection".

But for XBMC on Windows XP, the thumb/fanart for same library is coming up empty - how do I fix that? I could browse to a specific file to use, but I have multiple collections and this would be tedious, and I also don't know where to find the thumb I want either (they seem to be scattered across multiple folders that I would have to look in one-by-one to find the one I want)

This thread can be disregarded - this is apparently a known bug

http://forum.xbmc.org/showthread.php?tid=81330

Apologies.