Several times I observed the following problem with SMPlayer 0.8.6 (I'm using Windows):
1. Load external .ac3 audio track for a movie (the movie itself is an .avi file, XVID) - it is being used while playing the movie;
2. Exit SMPlayer while the movie is being played (the option to save a position inside a file is On);
3. Start SMPlayer to play the same movie again - the play position is restored and no sound is heard, though the external audio track is shown as loaded.
I can hear the external audio track again only after I unload it and load it again.
I don't remember such problems with SMPlayer 0.8.5 and earlier.