Same issue happened to me and my friend. He had a bunch of thralls that suddenly switched aggro. This is what we have learned:
- Thralls will attack both previous owner and everyone else in the clan
- Thralls do not go back to the previous owner upon disbanding the clan
- The building ownership have gone to me (clan leader at the time) when disbanding the clan
- Thralls did not change ownership to clan leader upon disbanding the clan.