The Shared Custom Skin Problem

I was playing a normal Survival, then my friend asked me if he could join my world. I let him in. The moment he entered my world, my skin was changed to his own skin. Ok, so I thought the problem would be solve if I change to my custom skin back. After I changed my skin back, my friend's skin was shared with my custom skin. He then thought it was wierd too. He repeated the processes that I did. After that, the same thing happened. His custom skin was also shared to me. I attached a video about it. Please, tell me what was happening.