Blacklisting problems

My experience with the Duty Finder has been mostly positive. However as luck had it, I was paired with the same unpleasant as well as inept player twice in a role. When I tried to blacklist the player via macro, /blist as well as character search, only to get the "Cannot locate a character with that name" error. The catch? I already tried to blacklist them after the first terrible raid, and I still ended up in the same party as them anyway.

I would love to have a proper blacklisting system, in which we would not be randomly paired with people who we have already blacklisted on Duty Finder, too. I know it's hard(er) as it is cross server, but I don't think it's impossible and lots of people would appreciate it.