I have the same issue You should have this issue with every Earphones you will buy except the jacks which are oversized in diameter which means the cheap ones. There are no pins inside the connector to hold it back from sliding out or i did not see them (tried to get a look inside with my flashlight).
On my classic mbp and I have a stereo mini plug to rca adaptor that refuses to plug fully into the mac outlet no matter how hard i force it. I'm not entirely sure why it will not go in. I compared its tip to another stereo mini that does work and it seems like the head is ever so slightly fatter, but not by much. Not sure if this is the cause or in any way similar to your situation.