I fixed a random Bug with the GUI, which caused it to not properly display the Items. And i currently cant setup a SMP-Server, as i have only one Computer running, and when i connect to myself (via minecraft_server.jar as LAN-Mode isnt working), i have no Issues with the GUI's.
Is anything else except the numbers above 2^15 broken?
Yeah just the number thing. If you setup a lan server it's pretty easy all you do is java -jar server.jar and then when you connect to it you just do 127.1 and should connect to it.
I could test up just a basic test server if you like just so you can login and see with IC/yourmod