Start SwingSet2, switch to Gnome L&F, go to Button Demo/CheckBoxes
There's still a problem with the images when pressed, but this is
not about it.

Uncheck 'Content Filled' checkbox, and check it back again. Now
click any of the Checkboxes, and when checked, they will have a different
bg color, which stays on even after mouse has moved from the check
box.
This doesn't happen unless you check and uncheck the 'Content
Filled' checkbox first.

This is with mustang (b04), but the bug has been there since 1.4.2.

I've attached a screen shot.

###@###.### 2004-09-27