Skype: Shared Input/Output Audio picked up by mic

Hi, I hope someone can help me with this or verify if it's working as intended.

Sometimes I use Skype on my MBA"13 with a headset/mic to talk to friends and recently found out the person on the other end can hear the output sound from my headset (Volume up/down or music playing in the background).

I tested this on GarageBand by recording voice and it did pick up any sound my laptop was making. I'm guessing it might have to do with the shared input/output port but the lack of anyone mentioning the internet (for mac) makes me think I have some settings wrong?

Can anyone tell me if this is normal or is there some option I can change to stop it?


P.S. This is not the case of the mic picking up background sound from speakers. I am using a headset with an inbuilt mic.

 

I'm currently using it with the iPhone 5s Handsfree for the headset and mic. The mac is a MBA"13 (mid 2013).