I had this bug before in the web version and now it shows up again.
Not all words i insert falsely aren’t added directly to the difficult wordlist, but show up the moment i normally review them (at that time correctly).
So I make for example 10 mistakes and get only 5 words to the difficult words.
The next day I repeat/review my words (where of course all these 10 words also appear).
but even after completing these words all correctly now the ‘other’ 5 words appear afterwards in the difficult word list (so the missing 5 ones from the day before).
It isn’t that annoying of a bug, but it is not working like it should.