Mac playing output sound into microphone when using earbuds

My mac is constantly playing any output sound into my microphone when I'm using my Apple earbuds. This means that as soon as a sound is played it's transmitted on Skype when I'm in a call. It's as if I would have had Soundflower or similar software enabled, although I've made sure I do not. I've also made sure that the issue only appears with the earbuds.

I've verified that it has something to do with the combo sound port (I'm using a 2013 MacBook Air) since if I plug the headphones in half-way I don't have the same issue but then only one the left side speaker works because of how the connector is set up.

Basically this guy sums it up perfectly but sadly several years have past with no replies: http://ift.tt/1ACuMh6.