Spotify issues while on a Skype call

[daoline]

I have an odd problem, sometimes I listen to my playlist while I am on skype, but not loud enough for the other party to hear it, which they can't. However, I have started using headphones so they can't hear it at all, I can hear them and the music just fine. But even WITH headphones on, if I talk while listening to music on spotify, my voice goes out and anyone I'm on a call with can't hear me. I experimented with this with music on my computer and it doesn't cause the same problem, neither does watching videos on youtube, so it seems to be something inside of spotify. What is causing this and how do I fix it? Also, the volume of the music doesn't matter, it can very low and I still cannot be heard...even though my skype friends can't hear the music at all...as it is over headphones.