Are you using the beta version or version 3.5?
Stage Traxx 3.5 will play all songs within a playlist. So if you select the last song and the playlist has autplay on, it will continue playing from the beginning until you reach the current song again.
Version 3.6 will continue playing that playlist indefinitely as the autoplay playlist mode is usually used for break music and you don't want to worry about the background music stopping at the end of the playlist.
You can work around this by using the autoplay feature on individual songs. Then you can omit autoplay on any song you like and playback will stop there.