Leaving shouldn't be a problem. It's the sanctity of "home" that prevents them from going in without the invitation. Those boundaries are meant to keep bad out, not in. That even applies to some of the rituals and prayers used to bless a home in general. They're usually phrased to bring good, and bar bad.

Then there's also the fact that if you build around the vampire, you've made it part of the home, they no longer need an invite because they belong.

Back in the older myths, there's no mentions of rescinding an invitation at all that I ever ran across. That's a very modern concept. I'm not certain where it started tbh, it's been years since I was deep diving vampire stuff, and I wasn't particularly paying attention to when things came around as much as the various myths existing. I was into it out of a combination of personal interest and gathering ideas for world building.

I wanna say that the idea of a rescinded invitation expelling the vampire was brought into common thought in the movies, but I'm damned if I can remember for sure. Nor where it showed up first. My memory says it was somewhere in the eighties horror boom, but that might have been preceded by literary invention

Now, if I was writing vampires that had to be invited in, I like the idea of the "magic" of home being powerful enough to physically expel them. But I tend to like to base my magical effects on something historic (No matter how loosely applied) when I can, and I'd likely use the basis of the foundation of the home being the seat of the magic. So I still wouldn't apply the effect to a foundation built around them. They'd be safe inside the boundary until they left.

At most, I would have them feel uncomfortable there. Reason being for that much that the "life" of the home would be rejecting them. That's a concept I've played with a little as a DM/GM before.

OP is the correct answer. The reason vampires can't enter homes is because of the positive mental energy built up around the house as a threshold. Giving consent to a vampire to enter is allowing them a pocket through the threshold. Said threshold is built up through regular living. A family home with a stay at home mom and three kids will have a stronger threshold than an apartment lived in by a two-job worker. Some stronger vampires can break through weaker thresholds (depending on source). There are multiple supernatural beings that this threshold can (supposedly) stop, not just vampires. So just because someone else tells them they have legal permission to enter a home doesn't mean they'll be able. It's magic, not legality.