I think I found another bug.
I created a custom preset that only includes kanji, and this worked fine enough, but after finishing a set and clicking on “New Quiz”, it no longer limits the selection to just kanji and instead seems to load all kinds of cards. To work around this I had to manually switch to a different preset and back to my kanji-only preset. I’m also using the Additional Filters script.
EDIT: Hmm, odd, this seems to have happened only once? The second time it worked just fine so maybe just a one-time bug.