Server crashes when hitting "Multiplayer" in the client

Everytime i try to join my fresh updated server, the Java VM on the server falls into a loop with the messages in the screenshot below. I just have to click "Multiplayer" and the client tries to get a connection to the server, the server crashes. The messages don't appear in the log files nor in the crash-log files. But i can stop the server normally with 'stop'.
I think it's something with the new optimization in the network code Searge mentioned in some tweets. In 1.8 everything works fine.
Maybe the changes aren't compatible with older Java-Versions?