I run into this problem too while working on improvements of my app where I wanted to make the camera preview a bit smoother. Instead of closing it down if not needed by stopping the preview and making the surface invisible I only stopped the preview and left the surface visible. (this makes a nice still image and has a shorter restart time) This caused the “Leaked 2 GPU objects!” crash if the app became closed.
I assume there are only two situations where the preview is closing clean: a) if the preview is running b) if the preview is stopped and! the surface is removed from view (invisible).