iPhone's hold button causes skipping in currently playing song
I have seen failures of the digitizer think that a finger was depressed when it was not. Usually it's some odd noise or interference and shutting down the device and then restarting it clears things up.

You might also be able to detect that by tapping a calculator or other app that shows when a finger down event happens on pretty much all the screen.

Of course, if you have a hardware issue, this won't fix itself and it will typically get worse over time rather than better.

Additionally, on the iOS 6 - there are some times when I've seen the system get really busy with background tasks such that music player doesn't get the CPU it needs - especially when iTunes Match is enabled and the device might need to go out to the internet to get a song or an update to the catalog, etc…

You can diagnose software issues by putting the device in Airplane mode and powering it down (hold the sleep wake button and slide to turn off). When it starts in Airplane mode, all running processes are only local ones and you can then test the music player and the screen to isolate the device from the internet before re-enabling Wi-Fi and/or cellular data until you've gotten a feel for whether the issue is software, hardware or something that was corrupt on the running software and a reboot cleaned that up.