Also, the jackets on those tiny Ethernet wires can melt if there is too much heat. I had the same issue on one of the inputs and found that I didn't unravel the twist enough on one of the wire pairs and while soldering to the jack caused the melting of the jackets to the point where the two copper wires ended up touching each other causing the short. It was difficult to see by eye because it was totally concealed. You could unsolder the wires from the jack and see if the jackets are fused together.
