My guess is that this is what's happening. With うらみ, you were previously studying it with hiragana and meaning only. Got those levels up. Then, when you learned the kanji, renshuu says "ok, they know the kanji, let's start studying the kanji-specific vectors for the word". As you had not yet studied those, they come up immediately.
Thanks! That confirms what I thought. Because of the new kanji, both that top one (Kanji > Kana) is becoming active, and the "Japanese" for the other two switched from kana to kanji. So, both the mastery appears to drop to 0 (because it is no longer considering the kana vectors), and it jumped up for review (since the kanji vectors were unstudied up until now.)
Excuse me, I don't understand this technical details. So, I do need to study kanji for some time or do I need to enable that vector? Because it just add words for vocab schedule and I waste some time to answer terms that I already know. If it confirmed as a bug then I am sorry for being impatient.
Sorry for the delay. Yes, once you learn kanji for the first time, you will need to study words that have that kanji in them a bit before the reviews for those terms start to slow down.
I have the same problem. Some of the words I had at level 9 dropped to level 1 once I started doing a new kanji schedule. Is there a way to keep learning new kanji without losing the related vocab mastery?