I was using sports tracker and the factory installed MP3 player (music). Changing between them while out on a run. After a while, the sound controls on the side of my Z10 stopped doing anything. Even when I went into the app itself, the phone still did not seem to recognize or care that I was listening to music. The strange thing is that a few minutes after this issue started, the volume muted, as though a bunch of sound volume decrease messages were processed by the OS. thing is, after that happened, the volume control stil ldid not work. Ultimately, I had to reboot to get this worked out.