I've always been a big fan of the flash cards, but lately, when I do study all, I get quized on tons of words which I have never seen before! Sometimes they are random difficult vocabulary, sometimes it's literally a card with no audio with "--" on back and front.
These words seem to be mastered words according to the program, because hovering "okay" or "well" will tell me that the word will be reviewed again in over a year or something.
Considering I carefully select what new words to introduce, mostly by importing from lessons I've listened to and know already, there is no reason for random words to show up.
I tried investigating and I found in some of my decks, words had randomly been replaced. Beginner lessons which originally had easy vocab like "Nice to meet you" suddenly have vocab like "To lose one's mind" and other random words way beyond the level that I need to know. These words which I have never learned before are listed as mastered and appear in place of the vocabulary which I actually know. How did this happen??