There seems to be an issue where the names of characters in your guild outside your own realm start to become duplicated when displayed in the guild character list and chat log. It seems to progressively build up over time, as the most extreme instance I saw screenshotted from a guildmate had 16 instances of Dalaran attached to my name on their client.
I believe this to be related to the caching of character names, as deleting the Cache folder in the WoW retail directory resolved the issue for me. It seems likely that it will start to build up again, as I did not see it the first two weeks of the patch.