Betty only closes up her den for molting, too. She does sometimes do some re-arranging at night and make the entrances smaller, but not completely closed. The entrances are usually wide open in the morning. I suppose it depends on her level of ambition that night. It's not consistent. She hasn't been doing it much lately. She does have the rocks in front of her den just exactly how she wants them and if you move one, she puts it back. She regularly redecorates her entrances.
Bonnie does the same thing. Keeps her entrance very "tight". I put some rubble in tonight and it was almost like giving a 2 year old a sucker. She came out and started construction right away.