Lol this is obviously what people will do to try and cheat the system by loading into each others layers.
Dude I see you a mile off…
Honestly who cares about players like this.
If your mate is in the dungeon and you cleared the first room of elites then just let them join. Kill the pack of elites again, but how annoying is it going to be having to have tons of people to switch layers to.
Maybe you have 4 people who are doing this. 4 cheating losers btw. Ok fine but they still only get 4 packs of elites before each world has a dungeon in it that hasn’t been completed and needs to be before it can be reset.
I think this is a pretty good measure.
I’m very happy about this as it was literally something I gave a bug report about.
Get rekt exploiters 
Tiny cellars should not be able to be reset ever. Especially after buffing them.