Ya, that's legal.
It's no longer a parcel once a building is placed on it. The only real reason you keep your marker on that building is to remind yourself that you are the person who has the right to upgrade it...no one really "owns" that building...so anyone can connect to it.
Hope that helps!
Pretty much clears it up.
Thanks. That wasn't 100% clear in the rulebook.
So upgrading to a building is kind of dangerous then as other people can start connecting from your lots. Eesh .