Does Dev_GLobals::CommentEntry appear only once on your layout or could it be that you have more than one copy of this field on your layout?
Hmmm...will double check that..
Ding ding ding! That was it! And that also explained why the side scroll would jump to the right quite a bit when running that script, too: I had left an old copy of the field off to the right, in the non-layout area. That is apparently the one that it was going to and entering text into, which would then show up in the other instance of that field once you clicked into it.