Imperial Ground doesn't mean we have conquered it. We can rent things and call them our ground. It's quite normal. Ever rented an apartment?
It's not normal to have a person threatened to death for entering, but since we consider we have rented it, it is normal that we act protective towards it. I've seen many guilds take spaces before, like the Felines Lair, and the Survivors of Vaern that share that same place with us.
If you think it is not allowed, please, do report it to a Game Master. We follow the rules and we'll do as any person from the DE team tells us to. None of you, however, has the authority to to tell us to move though. I believe some of you might be as childish and frustrated, since you can't bother or get the Empire's attention in any other way, as to actually use out-of-character reasoning to importunate us with pseudo in-character actions. We don't mind. Unlike some people, we do know when to report to Game Masters.
EDIT: Yes

Don't make me feel worst than I do -_- Someone delete that thing. I'm so not used to having two accounts in one forum...