I have noticed that when people use guild chat, when someone chats the bubble will appear randomly over another guild members head.

Last night a member of my guild who was in a level was chatting on guild chat, and it appeared as a bubble over the head of someone else in my guild. We were in a completely separate level.

Another instance... I was in nuri town, just standing there and another one of my guildmates was using guild chat, and the bubble appeared over my head. Only guild members can see these bubbles over the heads of members in their own guilds. Other players not in the guild will not see the bubble (the text is green in the bubble). It's just a sorta weird thing.