Happens to me all the time, you just have to wait for your character to realise it needs to sign out and then you can log in. Literally happening to me right now
I happens to me only once. I only need to wait 10 or 15 minutes. My 2 ctvs: on web site, my player was 'green' as connected instead of blue. When it turns back to blue, I could connect again.
This is kind of like 'Wile E. Coyote' hanging in the air for a while before realizing he should actually be falling down. It's a result of the game's network protocol trying to be efficient.
Once someone was standing there with me and they quit talking to me and they quit walking around. Then it said that they left but their character was still standing there. It disappeared after maybe 30 seconds. I bet this is what happened and it took it awhile to log out.