Shoutbox

in your screenshot, the icon makes sense (-> The light blue border around the icon)... But on the default XP theme it looks like shiit because the titlebar is already lightblue, and the "titlebar" in the icon seems like an error in the iconfile itself on that theme...

So for us the white wasn't the background of a window (which can be seen in your SS), but a non-transparent background in the icon itself. And the dark-blue bar across the icon seemed like a bug in the icon. (while in your SS it is clear that it is a titlebar of the window)