stylesheet background color for QTreeView breaks windowsvista style

Put a QTreeView in a QMainWindow, then use a stylesheet to change the QTreeView's background color. If you try to move or resize the window with the mouse, and the style is windowsvista, the application blocks. It looks as though the mouse is being grabbed and not released, because if you hit Ctrl-Alt-Del to get Windows’ attention, and then hit Esc, it unblocks the application.