Keyboard input is not working for me when the game first starts. I start the game, press create new world, and try to enter a world name or a seed name, but nothing happens when I press the keyboard buttons to input a name. Mouse input still works.
If I load an existing world then the keyboard works fine while in-game. If I use the "exit to menu" option after loading an existing world and then create a new world, then the keyboard will work as well for inputing a world name/seed. So it would seem that something changes when a world is loaded.
I have the same problem with another LWJGL-based game (revenge of the titans) so it might be a LWJGL problem. I've had this problem for a long time, at least 6 months, maybe longer. I can reproduce the problem every time.
I did some more research and it turns out its a bug in the window manager I'm using, and not in minecraft/lwjgl. This issue can be closed.