Don’t know if anybody else noticed yet, but posting here just in-case.
Do you mean leaving via the door or leaving via disconnecting? If it’s leaving via the door, it’s intentional to have you go back to your previous plaza server since your condo is linked.
This happens when leaving a minigame too. (Ex: If I join a minigame from a plaza, and my friend joins me, I will exit to the plaza I came from and my friend goes back to a different plaza that he last connected to.) I believe this is more of a feature than a bug though.