Hm. I just tried it myself, and I have the diagonal lines, at the lower right corner of the blank review window. I'm going to assume that you tried the usual log out and back in again, clearing cache and cookies first trick, which often resets these sorts of things.
The only other suggestion I have is less practical, but you can actually write a review in your word processing software, and copy and paste it into that text box. That way you can see what you're writing.