Multiple windows - destroyWindow hangs

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I have a MFC C++ slideshow program that I've written, which uses a thread to display images on a secondary monitor.

I just added code to also show the same image, scaled down, as a thumbnail on the primary monitor. However, when I call destroyWindow(), the call hangs.

The code is as follows:

    destroyWindow(SCREEN_TITLE);
    waitKey(1);
    destroyWindow(THUMBNAIL_TITLE);
    waitKey(1);

I added the waitKey after reading that suggestion in another forum topic, but the second call to destroyWindow never returns??

Also - the second window has an aero cursor, while the first window has cross hairs.

Any help would be appreciated!