The + icon shows up (with no square, so it doesn't think I have the card already). I can add the card with it, but it doesn't give me any sort of notification about a duplicate card, which it is (I created a test category with the words 眼 and 脸). So now the card category has duplicates and the characters still don't highlight in the reader even after exiting and reloading.
I'm not sure if format history is working correctly for me. It highlights most characters for my lyrics document. I just now downloaded Ah Q and it seems to highlight a lot of specific words, but I'm not sure what the pattern is. For example, it seems to highlight every single 的, almost every single 是,and every single 一 (but not 二). From the name I assumed it highlights recent changes to the document, so I added the sentence, "我是一个很好的学生." It highlighted 是, 一, and 的. This doesn't change between "any time," "today," and "within X days."