Hello,
This, I believe, is a bug that I noticed a couple of days ago... To reproduce it, add a track to the playlist *twice* followed by several other tracks. Start playing the playlist and once you get to the track that is repeated twice, subsonic plays that track endlessly. It just keeps repeating that same track until the user manually moves to the next track.
I am using Subsonic: Version 3.7 (build 898) – June 15, 2009, Server jetty-6.1.x, java 1.6.0_16, Linux (20.7 MB / 63.3 MB) on Ubuntu 9.04 Jaunty. I will be happy to provide any other information necessary.