http://bugs.winehq.org/show_bug.cgi?id=9969
--- Comment #4 from Mikolaj Zalewski mikolaj.zalewski@gmail.com 2007-10-12 13:32:45 --- The window is created without WS_POPUP nor WS_CHILD so CreateWindowEx adds WS_CAPTION (the parameters to CreateWindowEx are WS_CLIPSIBLINGS|WS_CLIPCHILDREN, WS_EX_TOPMOST|WS_EX_NOPARENTNOTIFY). This makes the window managed in CreateWindow - before WM_CREATE is sent. After CreateWindowEx returns the application uses SetWindowLong to set the style/exStyle to the same values it passed to CreateWindowEx what clear the WS_CAPTION but the window is already managed and stays so.
Later the application seems to process the WM_NCCALCSIZE and add a 16px nonclient area at the top to draw a caption but that probably doesn't affect this problem.