Ubuntu window randomly stop drawing

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http://askubuntu.com – After using Ubuntu for a while, application windows will begin to stop drawing. The application will continue to run (if I'm using keyboard shortcuts, the application exhibits normal behavior, like saving files and opening popups), but certain windows just have no content in them. An example screenshot UMongo has a window, but nothing inside is drawing. This behavior is not limited to this particular application, and I've seen it happen to virtually all applications on my system. In this example, the process in question was not frozen, System Monitor tells me that about 50% of memory and (HowTos)