A crash occures when you type in "/blacklist add" and type enter.
Not sure if this occures for everyone, but so far everytime I've tried, the game has crashed.
I found this as I was looking for a shorter way of adding someone to my blacklist.

Time: Today, at around 12.21 pm, gmt+1
Frequency: So far 100%
World name: Moogle
Character name: Enuin Rose
Class/Level: Conjurer, 2
Party or solo: Solo
In-game time: Unknown
Area and coordinates: Gridania, Anywhere
Steps:
1. Open chat
2. Type in : /blacklist add
3. Game crash