One of our staff called me in to "fix" her project in Vegas 13. She had inadvertently switched into the A/B mode and didn't know how to get back to a single timeline. I made the change but discovered that the image of a single frame of the project was frozen -- stuck -- in the preview window, as though it were a still frame .png file.. Moving the cursor up and down the timeline did nothing to change the frozen image and no matter where I placed the cursor on the timeline the image persisted. However, if I hit the space bar or Enter key the project played successfully. Stop playback, however, and the "frozen" image returned.

I saved and closed the project and rebooted. When I reopened the project the Preview Window had returned to normal. My best guess is that the Preview Window has a buffer of some kind that was cleared when the computer was rebooted. Anyone have a similar experience, or a suggestion as to why this happened and whether it's possible to clear the Preview Window without rebooting?