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I would suggest checking if the item is visible

http://msdn.microsoft.com/en-us/library/windows/desktop/bb775044(v=vs.85).aspx

because if its not, you cannot get the rectangle. You can also...

I've had the problem, it appears WM_THEMECHANGED is only sent when changing from "having a theme" to "having no theme". As you probably want to call CloseThemeData and attempt to open a new theme...