well we sort of need to see more of the window to be able to determine whats going on. I don't think its borders because to make a border that thick one would have edit the borderthickness which means he would know where that was in order to get it happening in the first place. Windows Live Messenger by default does not have anything like that happen to it.
The only thing I can think of right now is that hes editing another skin and doesn't know why its coming with that white bit. If thats the case I hope you asked permission first
But yeah if it is like that wed need to see more of the skin to know whats going on.
/ 
