Hi Ron,
Welcome to The PainterFactory!
To answer your question:
Yes, that's happened to me sometimes and I don't know why. It shouldn't happen at all. The best I can offer is to say that in the past it has helped to close Painter X and wait a few minutes, then relaunch and try again.
Other things that may help are to close other programs while running Painter, avoid working too long without saving your files, closing Painter, and relaunching and sometimes even rebooting helps.
For a more expanded list of suggestions, check this thread at the Conceptart.org Painter forum to learn how to keep Painter running smoothly:
Keeping Painter 6 Through Painter X.1 Running Smoothly - Updated February 6, 2008, by Jinny Brown
Hopefully, someone from Corel will have a more precise answer but to me, this feels like a bug that needs to be fixed.
Cheers!