Setting Sleep Timer > End of track isn’t really accurate when Sweet Fades are enabled. It stops playback either a bit before or a bit after the track’s over, and fades the next one into it. Probably FF into the currently played track makes this worse.
The expect behaviour is to stop playback exactly at the end of the current track, without playing anything else.
@OttoKerner in response to [Implemented] stop playback after current track