This has suddenly happened and I don't know what started it. Whenever I want to view an avi file in the TRIMMER which I have selected in my avi folder by double clicking on its thumbnail, this action opens in the PREVIEW WINDOW an entirely unrelated event from an entirely unrelated avi within my PROJECT MEDIA window.

Fixed: Open media in trimmer wasn't selected in preferences. How does that become unchecked is another strangeness.