fullscreen mode breaks in xfce when coming from a maximized window

When switching to fullscreen using QWidget::setWindowState() leaving the already set maximized bit untouched, the fullscreen mode breaks as soon as a widget in the layouted window is changed. The result is a window with the geometry of a maximized window and the (non-visible) decoration and behaviour of a fullscreen window.
This only happens with xfwm4 as window manager and only with Qt 4.8. It worked with the combination xfwm4 / Qt 4.7. If the window has no layout it works.
Attached to this report is a Qt creator project that can demonstrate the issue. Start the application, maximize the window, then click on "Toggle fullscreen". At that moment, fullscreen mode works. Click "Set label" to display the current window state. This breaks the fullscreen mode. If you rid the window of the layout, the fullscreen mode doesn't break.