Windows 7 64 bit with 64 bit Blender
Broken: 2.76.2 fbca69c
Short description of error
Drivers do not work, when they are inside a node group.
(Didn't test it outside the compositor.)
Exact steps for others to reproduce the error
The value node on the top left (labeled "#frame") has a driver which takes the current frame number.
The group node below contains a value node also has a driver, and should output the current frame number. But this does NOT work.
So you can see it, if you render, the output of the group node is displayed on the left; the output of the (ungrouped) value node is displayed on the right.