Is this normal when listening to music?

[waly01]

I've started to notice that sometimes when I listen to either my touch player and songs on my storage or Pandora that if i hit the power button and put the phone to sleep sometimes the sound will just stop coming to the headphones. I've also started to notice that if the phone is close to full battery 60-70% and up it'll continue playing while screen is off but if the battery level is lower it'll stop.

Anyone else have this happen to them? I'm wondering if this is a battery saving mechanism or there's just something buggy with my specific device