I'm having a similar problem with my sorceress Jenna Gale. In-world now she appears to me as Maeve... her pixie familiar's name. One thing I did that could be involved: when I was possessing the pixie during a dungeon run yesterday, I noticed her (the pixie's) talk to the party was showing up as Someone, so I introduced her to everyone as Maeve. [=c introparty Maeve] I'm checking with others of the part to see if they saw a change, but I didn't see myself renamed at the time. On login today though, Jenna shows to me as being named Maeve.. the name over her head and on her character sheet. A double-check logout showed me she is still Jenna Gale in the server vault. I tried to use the above action to reverse the issue and get her named back to Jenna Gale, but it didn't work, so it may not be the actual cause. I just thought it couldn't hurt to report.
Edit: some while later, after posting the above, I saw her name was back to Jenna Gale. It definitely wasn't when I re-logged in. Unless someone logged in as a DM and set it for me or something, when I wasn't looking, then it does seem to be changing from the above method.. but after some interval that I don't know what is. Maybe a system auto-save or something.