I remember my friend and his brother wanted to play on I think a racing server, my friend could join but his brother couldn’t however if we went on my server or another person's server both of them could join in. I asked the host about it and he said that its an add-on that prevents two or more people joining a server with the same key, he didnt say if it was private or public.
My question is why is this add-on allowed if it technically is "breaking the game"? The rules on the blockland.us website state that more than one user can a use a key as long as they are in the same house, so thats nice and dandy when you go to purchase the game but then find out that because of a user made addon you can no longer use that feature which is part of the game.
The other people using the same key can be differentiated by clan tags, so I really dont see the problem.