I am fairly sure this bug was supposed to be fixed in the latest snapshot, and I know there are some resolved bug reports stating almost the same thing, but I still have the problem, when trying to join a server/LAN world while offline using an email as account name, or have a modifed team in the world, it still gives the:
"internal error: java.io.IOEception: Recieved string length longer then maximum allowed" error.

Fairly easy to reproduce, simply login with a name longer then 16 characters, such as the migrated account's email, and try to join a LAN game, or server.

another way to reproduce is to put the scoreboard.dat file that I am trying to use on my server into the world/data folder, host a LAN world, and have someone else try to join it.