I'm currently using Ubuntu 13.10
Every time I start Spotify or Spotify changes track Skype turns to offline.
For Skype calls I'm using my phone, but for chatting the computer keyboard and big screen are much more convenient. If I make a longer lasting chat, I just can pause Spotify and it won't turn my Skype offline, but every time track change (or possibly other Spotify) event occures, Skype turns to offline state again.
This is quite annoying as you could imagine. Sandly I haven't found any cure or hit to the cause of the problem. WIth Ubuntu version 13.04, there has been no problems
Spotify: Desktop 0.9.4.183.g644e24e0 Proffessional account
System: Ubuntu 13.10 x86_64