A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
I figured out what made the thumbnail panel come back. It's ridiculous, and feels a bit like black magic, but it's simple and it works consistently. First, click on the Normal view icon at the BOTTOM in the status bar. Then click on Slide Master view. Behold, the beauty of thumbnails! I would be very interested to know if anyone can replicated this result.