DestroyWindow must be called for tooltips in the OnDestroy Message Handler of the Dialog

It seems, there is an internal Windows Mechanizm which turns off the WS_CHILDWINDOW style even if it is set for the tooltip control (Traced by SPY). Therefore it is evident, like Jacques said, the tooltip control is not treated like a normal child window of a dialog and it doesn't get destroyed when the Dialog is destroyed.

Therefore, DestroyWindow must be called for tooltips in the OnDestroy Message Handler of the Dialog.