This is a known issue with Plus! windows. I experienced it too when I was fiddling with my translation system, but it seems like Plus! Live adds the title bar itself.
Well, I'll use this thread then for a
suggestion to Patchou:
Make the windows so that when a SetWindowText or WM_SETTEXT is received, check if the original XML defined a title bar so Plus! will only change title bars instead of adding them. It would be much more interesting for us, script developers!
/ 
