That's strange. Have you tried different browsers, to see if this is a browser-specific issue?

We tried it on

Safari (Mac) - current version
Firefox (Mac) - current version
Safari (Windows) - current version
Firefox (Windows) - current version

We tried it on different platforms (Mac / Win) and different computers. Everywhere the up / down keys do not work.

It SEEMS to work in Internet Explorer...

Maybe there is some kind of conflict with the Javascript or CSS in your theme?

I've tested this in Opera, IE and Firefox and it works as expected. It's just a textarea. I'm not exactly sure what would prevent the up and down keys from working ...