receive.denyNonNonFastForwards not denying force update

At eclipse.org we wanted all git repositories to disallow non-fastforward
commits by default. So, we set receive.denyNonFastForwards=true as a system
configuration setting. However, this does not prevent a non-fastforward
force push. If we set the same configuration setting in the local repository
configuration then it does prevent non-fastforward pushes.

For all the details see this bugzilla, particularly comment #59 where we
finally narrowed this down:

https://bugs.eclipse.org/bugs/show_bug.cgi?id=343150

This is on git version 1.7.4.1.

The Git book recommends setting this property at the system level:

http://git-scm.com/book/ch7-1.html (near the bottom)

Can someone confirm if this is intended behaviour or not. We ended up
using a script to set a local config property in each repository, but
with several hundred git repositories it would be much easier if the
system setting was honoured.

Thanks,
John Arthorne