I have had some issues in guild today whilst otherwise still enjoying the guild as a whole. So I decided to ignore the one user and go about my day. Well... The person did not end up being blocked as I had hoped and expected. I could still see him chatting in guild chat and got frustrated and tried reblocking him. Tried restarting the client to no avail.
Blocking the general populace worked fine, even tested it with a friend to doublecheck. Was able to ignore him then when he got into a guild I could still see him in guild chat. I had him repeat the same tests on his computer and he got the same results.