I'm also having this issue, I came here hoping that a fix or workaround might have been found. Got the Phase III Minor Miracle achievement, tried to use the /title set command in a macro to change my title to Beata of the Firmament, and got back a "Unable to use that title" message. I can set the title manually through the Character page in-game, but not with the /title set command, either as part of a macro or by entering it in the chat command line.