The house keys are buggy.
Took me 2 hours to figure this out the other night.
I used the key generator, to create 4 keys. None of them work except the master key. Even for myself. I then changed the lock 4 times, generating a new key everytime. Then handed everyone their key and it work fine. Still working at this moment in time.
Changing the lock should make all other keys not work like freemen said, but alas it seems it does not. Guess I you want to block someone access to the house, you will have to find him and ask for the key back.
I am sure Orth will look into and hopefully come up with the answer. Below is the other thread where Bruenor seems to have also changed locks in a similiar way. See bottom of the thread.
Thanks Aragwen
http://www.layonaraonline.com/forums/forums/thread-view.asp?tid=2914&posts=15