On my home PC i tried with chrome and firefox dev edition (both most recent). There, in the theme options only the first form field is visible and the preview pane stays empty. Today I tried again on my laptop and everything is fine. The problem persists after a complete broiwser cache wipe. I have no idea what happened here, I dont even get javascript console errors. Sorry for bothering you, but this seems more likely to be something weird with that machine.
Daniel