I am encountering a problem in the Study mode: the first two cards of my "failed kanji" list are displayed without the "Learned" button, so I cannot transfer them back to the Review stacks. And with others, if I click that button, nothing happens except  the first card in the list is again displayed, but the failed kanji list is not updated.
I think this behavior occurred after I fiddled with some Greasemonkey script ("alter sequence" or "count kanji", I am not sure).
Has anyone got an idea of where that might come from?
Thanks.