On a fairly regular basis I have been running into definition prompts with characters that are new to me, where the practice page tells me something like "studied 4 days ago: overdue (737%)" even though I have never seen those characters before. This happened just now with the definition prompt for 滿, which came up saying I had studied it before; I had definitely studied its simplified version 满 before, but never 滿.
This seems to happen only with traditional characters and only with definition prompts. I suspect this is due to some confusion when I run into a new character and see its simplified definition prompt, which is somehow getting saved as if I also saw the traditional version.
James