I just hopped on a flight from Dalaran to Sholozar Basin with my Troll Horde Mage. I then logged out. A bit later, I decided to change that character’s faction. I chose to change her to Alliance Pandaren.
Once the service showed complete, I logged her on. She was immediately in-flight inside Stormwind, bumping into and flying through buildings. She flew directly north, flying through mountains like a hot knife through butter. I did click the Request Stop button a number of times, but that did not work.
The character made a left turn when she got north enough (north of Tirisfal Glades, across the sea), flew underwater at one point, then I got disconnected halfway in between Eastern Kingdoms and Northrend. I tried logging on a few times, and was able to, but my character was stuck in a void. I was unable to move or cast, and I would get kicked offline in less than a minute. I’m assuming the game was attempting to fly me to Scholozar Basin from Stormwind.
I chose the support option to unstick my character. It stated that I could end up in a place with an opposing faction, and I accepted. I then got kicked, and when I got back to the character select screen, it showed I was in Deathknell. When I tried to log in, it stated that “A character with that name already exists.” I tried logging in a second time and I ended up at the graveyard in Deathknell.
I guess the lesson learned is to not choose faction change while in-flight.