Playbin2 not surrendering hardware after play

[Jeffrey Barish]

My app uses playbin2 to play sound files.  Occasionally, after playing one 
sound file, I am not able to play another sound file because the device is still 
in use.  I used lsof to find out which app was using it.  It turned out to be 
my app.  I guess that something is not letting go of the hardware when it 
should.  If I wait a while, it seems as if the hardware eventually becomes 
available.  Most of the time, my app works perfectly.  Any thoughts about who 
the culprit might be?

I am using ALSA, but I let playbin2 use the default audio sink.  Might it make 
a difference if I were to specify alsasink as the sink?

I am using 0.10.36 on Lubuntu 12.04.

Jeff