… that the
~QX11PixmapData(): QPixmap objects must be destroyed before the QApplication object, otherwise the native pixmap object will be leaked. warning most KDE applications display when exiting is actually false.
The X server will cleanup any opened resources, including pixmaps, automatically when the client exits. This is much like how the kernel automatically closes files and memory allocations when an application exits.
(The QPixmaps in question are the ones cached by KIconLoader as best as I can tell. They are cleaned up, just not before QApplication’s destructor runs.)