Sorry, english is not my natural language, that's why it's not easy to me
But here i'll try to explain it better
With the device locked and music playing, get to the lockscreen. On it you have a "playback indicator", or "indicator bar" of the song you are playing (sorry, that's what i don't know the exact name in english, but it's the bar you use to see in what part of the song you are, and to foward it or rewind it. Do you understand?)
So, this "Progress bar" will be "locked" (it will show you the time of the song that was when you locked the device and won't move). What i've done, is to move the indicator to another part of the song, and it will work again, and if you unlock the device, the song won't revert to the poing where you locked you device.
There is it. I have tried to elaborate more the "solution".
I hope this fix your problem too!