Why does my iPhone do this?

I have an iPhone 4S 16GB on Verizon.

Whenever I have a song playing (doesn't matter if ripped from a CD or a downloaded track), if any button is pressed, maybe the lock screen after I turn on a track of song, the song either skips back to the way beginning, or to some random point in the song. Then the phone will start back to where it was playing when the problem started. It has now started doing this all the time, before it was just a little bit. I've restored and re-installed everything to no avail. It doesn't bother me excessively, I just wonder why it happens.

All of this started after iOS 7 upgrade, so I'm beginning to think that, that is part of what's causing this.