Am inclined to think that the vampire in question did not have the ability to ignore locked doors in cases where sims are sleeping. Having a resident vampire is no guarantee there would not be a break-in. Shortly after the pack came out I had a vampire/human household, a townie vamp came that had the ability, and the resident vampire was not able to intervene - no options to do anything available. Human sim was saved only by a fast use of the instant vampire cheat on her. Have used the 3 layered defense (locked door, garlic farm out front, water slide (they often like those)) since. Have the cheat in reserve for any leakers.