Whenever I join my friend's world, my skin changes into their skin which is not owned by me.  There is usually around 3 people over 5 who will have the same skin.  It happens randomly and only affects people who have skins downloaded from apps or websites (not always).  It's very annoying because we're not allowed to change the skin, it tells me I don't have photos.  When it works eventually and I pick my skin it will let me use the skin I was using or some other skin which is not mine and does not give me the skin I picked.