When Fred moved into the Hyperian, even though the hotel belonded to Angel, she had to invite him into her room (I can't remember whether she had to invite him into her cave in Pylea), and, once the home owner left in "Empty Places" in Season 7, Spike was able to come in where Buffy was. Fred thought of her room as her home whereas Buffy was only "looking for a place to crash." (I know what Spike said about "they" really having taken over, and that's why he could come in uninvited, but for the sake of my argument, I'm gonna just assume that he was wrong) Andrew was able to invite Angel and Spike into pseudo-Buffy's apartment, even though he says that he is only staying there because he burned his apartment up. Angel was able to enter kate's apartment in time to save her, even though she wasn't dead (luckily for her, she didn't need cpr, wasn't it?) Finally, Angel had to be invited into Lindsey's office, even though he didn't live there.
My point is, maybe whenever someone considers a particular place as their private spot, sanctuary, place of refuge, home, sanctum sanctorium, "my" place, or whatever, that attitude somehow forms a sort of personal shield, something like an expanded aura, that protects that spot from uninvited invasion by any mystical or supernatural force. In other words, what actually makes a house a home is more the attitude of the resident than who either owns it. Otherwise, an apartment, rental house, or hotel room would be exempt from the invitation clause.