I am having the same problem with my chapter buttons, except none of my thumbnails are changing at all. Normally, I wouldn't mind the first image in the chapter being displayed as the button thumbnail, but I have a completely black intro for one of them, so I just get a black button. When a right-click to select a different thumbnail, everything works perfectly except...NOTHING HAPPENS! Anyone have any suggestions?

Your problem has nothing to do with the 13 month old, dead thread, that you hijacked. The OP, and I, had/have a problem with Title icons not being retained, once the project is saved.

Your problem is with chapter icons. The icon for chapters, is going to be the frame, at the point that you created the chapter, as it should be.