It seems that the iOS 7 update introduced a bug that made the text window in app store reviews stop scrolling, so if your review is long enough, the text goes below the virtual keyboard and you cannot see what you are typing. Manually scrolling the window does not work, because it bounces right back to the same position. I have reported this bug to Apple's support team and actually got a response, but the next update did not fix the issue. Haven't heard from Apple since then. Did they forget about it?