I'm stumped.

I done this with three different projects, and it's consistant with every one.

I'm using the 'Fireworks' style for my base, but modified (I use a different background)

All chapter buttons allow me to access the 'Select Thumbnails' option from right-clicking on the thumbnail, but the first chapter never lets me actually change it. The thumbmail changes work just dandy for every other chapter.

Any suggestions?

There must be a bug somewhere. Does the same thing for me.

If this is a bug, you can post in this area http://forums.support.roxio.com/index.php?showforum=136 and the people that work on the themes can either fix it or explain the design better then myself.