If you use the pyramid to teleport to someone who is currently using the magic mirror, they seem to be teleported to the area which serves as the background for the creation screen. You can also see a bunch of other objects which are not meant to be visible during normal gameplay.

This happened on the latest version. We both use GOG.

https://i.imgur.com/xmprQIC.jpg

https://i.imgur.com/7kdi9Xs.jpg

https://i.imgur.com/quE5Q31.jpg