Twice now I have seen a shout from a player already on my blacklist. This appears to happen when I press O to blacklist another player. I have a screenshot showing this, but as it contains many player names on the open blacklist window, I hesitate to post it here. Please let me know if it is needed.

Time: 9/13/13 1:22am PDT
Frequency: Twice so far
World name: Behemoth
Character name: Cikala Silvercloud
NPC name:
Monster name:
Class/Level:
Party or solo: solo
In-game time:
Area and coordinates: Ul'dah
Steps: 1. Blacklist a player.
2. A little bit later, press O to open blacklist.
3. As I press O, a shout from previously blacklisted player appears in the chat window.