I'm getting a bug in Blender 2.63.13 r48178 where the internal render is not properly displaying the output of a Composite node from the node editor, nor is it saving a file defined in a File Output node.

The exact same .blend file in 2.63 r46461 (installed following http://www.noobslab.com/2012/04/install-blender-263-on-ubuntulinux-mint.html )
works properly: the render output shows the render node and also saves the file.

OS: Linux Mint 13, 64 bit, Blender 2.63.13 r48178 was installed from the Linux Mint distro software manager.