I am running SlimServer 6.5.0 with SoftSqueeze from the subversion repository.  Often, Softsqueeze hangs when stopping and re-starting a stream.  The problem seems to occur in the call to audioMixer.flush() (Player.java line 549).  The flush() method calls line.stop().  If it happens that the "mixer thread" is executing playSamples() when line.stop() is called by the flush() method, playSamples() never exits.  I haven't determined why this occurs, but I commented out line.stop() in the flush() method and the problem seems to have been fixed.  I don't think it's necessary to call line.stop in flush() since line.stop() is called elsewhere in the run() method.  I think there may be a bug here, but I'm not claiming that my solution is correct.