Just posted the 1.0.3 with a fix for that, hopefully that should be fixed up! Lemme know if you have any more issues.
Shouldn't be an issue with background transparency. Just to double check, you have it in the 'player/winpanels/' folder and you've named it the '(name in values.txt)trophy.png' exactly to make sure?
The first thing that broke it was it was looking in the game resources instead of the file directory which it should be doing and got it working unless there's another quirk.
(Edit: Annoyingly, it works fine in the debug version but breaks on export. Gonna have to look more into it x.x)