Black list functionality

I have had two instances now where adding a player to the black list does not block them 100%. Both times I was in Uldah. I saw the spam added the player to my black list. maybe a minute later I got spam again from the same player. Thinking I may have gotten the name wrong or it was slightly different I tried to add to my black list again and was told this player is already on your black list. I also though that maybe they had deleted and recreated which I could see if it was 5-10 min apart, but this was less than a minute so I highly doubt that was the case.