I was doing a Vocab schedule.
I've opened another tab and did 1 kanji review from the Kanji schedule, to show a screenshot to a friend, then closed it.
I went back to the Vocab schedule tab with the pending question, I've answered it and I got sent to the correct answer page for the kanji I previously answered in the other tab from the Kanji schedule.
Basically the Kanji Schedule overlapped the Vocab Schedule :S
