So I was building my house, and when I completed the door, I entered. My game crashed. Turns out, I couldn't make any more saves. From what I could find out from other people online, it might have been a mod conflict. Even after uninstalling *everything* except Hearthfire, and then uninstalling that too, my savefile was permanently unable to make more saves.

So I reverted to an earlier save, and only enabled Hearthfire. I went back to house building. I finished the house (The Dawnstar house), and entered it. Or not; Turns out Hearthfire is corrupting my save files all by itself.

So consider this a bug report.