The teams thing is interesting. It bit me a few months ago because a teammate accidentally registered for a race with the wrong car. He couldn't back out or join the race with the new team the rest of us registered with because he was already in a team.

I'm not sure why it's implemented this way, but given the issues with registration/session creation for the Daytona 24 hour this year I'd guess the team event registration is write only and doesn't permit updates in order to simplify the session creation logic.