By thumbs are you talking specifically about the image that is generated inside the player itself as a preview image?
If so my experience has been that it depends on the video. Many of mine i do get that on the page load where they are all displayed. But among the 12 on the page there are several that for some reason (header issue or whatever) do not.
That is why i worked with him, i did a mod to mine that allows a default image to be shown if the preview image is not there. So instead of looking at a black box player, you see a default image. That process works well enough for me but could be impoved im sure and so i sent it to him for that purpose, to take what i did and make it better.
We also put our heads together on the issue of IE9 player loads and thru alot of research and reading on my part and testing i did find what i believe is to be the solution and i also contacted him on that as well and gave him my information so that he could apply that in the upgrade as well.
I am also looking forward to seeing the results. :)