Today I found out that I had a large number of clozes marked as known that should not have been marked. I suspect that they have been accidentally marked by my fat fingers in the round history, when marking them as favorites; the minuscule buttons are placed side by side. Similarly, in the round results overview, the favorite button is just beside the ignore button. This is especially problematic when playing on a mobile phone with its small screen.
My suggestion is that marking a cloze as known or ignored should require a confirmation when activated from round results or round history.