How is an avatar able to enter a private parcel with public access turned off?

[ShirtlessTicklishTx]

Only minutes before I discovered that a day-old avatar had rezzed objects without permission on my sim, another older avatar was able to come into our private parcel and stay for more than a minute even though public access for the parcel was definitely unchecked and even though the avatar's name is most definitely not on the parcel access list.  Why did the avatar not encounter the yellow banlines as was supposed to be the case and how was the avatar able to enter the parcel anyway as should not have been the case?