Minecraft uses LWJGL and the LWJGL library have some issues
working properly on Java 7 and Mac OSX Mountain Lion.
Apparently it is something with Java 7 dropping support for the way
they handle drawing (something to do with limited AWT support for
hardware accelerated canvases or so).
LWJGL used to be able to get a 'NSView' from the AWT Canvas and
stick a NSOpenGLContext on it, however this is not possible anymore.
They've done some research and got it to work in applet-mode using
CALayers but this was rather slow as they had to render to image
using a pbuffer and it then draws the image on the CALayer.
For their stand-alone native window an additional problem is that
the window is still created through Carbon rather than Cocoa
(which might be able to give the NSView handle).
and relevant code: http://java-game-lib.svn.sourceforge.net/viewvc/java-game-lib/trunk/LWJGL/src/native/macosx/
the 7u6 RT has marked this as NMI
Please get PM (Aurelio Garcia-Ribeyro) involved.
We would need to see some plan for how we are going to work to get this resolved, or if there are workarounds that are viable for 7updates.