http://bugs.winehq.org/show_bug.cgi?id=29474
--- Comment #3 from A Wine user RandomAccountName@mail.com 2011-12-30 05:05:31 CST --- Created attachment 38174 --> http://bugs.winehq.org/attachment.cgi?id=38174 Partial screenshot with native comctl32
Do the icons in the application look any different for you after winetricks comctl32? Native comctl32 should cause them to display without transparent backgrounds due to some incompatibility. If they still look the same, Wine might not be loading the native one for some reason. You could also try running it with WINEDEBUG=+loaddll to see whether the native one is ever loaded.
If they really don't work for you with native comctl32, I can't explain the inconsistency. This screenshot shows how it looks for me with native comctl32.