--- Operating System, Graphics card ---
Mac OSX Snow Leopard,
[more information attached in "system-info.txt"]

--- Blender version with error, and version that worked ---
Crashes in current official version: v2.68.0 official, r58536
>> it does crashes in previous versions too, e.g. 2.67b
>> Commands apparently different as far back as v2.62, v2.65, so raises usage error (different)

--- Short description of error ---
As described in the text editor of the attached blends, certain use of the group_instanc_add operator through python instantly crashes blender or doesn't work (no error). This includes the same method the info bar claims to use when done via the UI (which does work without issues). There is at least one way to successfully run the command without crashing or exceptions, but it does not match the documentation or info log.

--- Steps for others to reproduce the error (preferably based on attached .blend file) ---

The attached blend just has one cube as a part of a group called "g".
The lines of code and how they behave if copied/pasted into the console are in the open text document.

Blenderartists thread:
http://www.blenderartists.org/forum/showthread.php?306855-Instant-Add-Object-from-python-cancelled&p=2465388&posted=1#post2465388