Network Manager networking disabled after suspend

[Patrick Wiseman <pwiseman@gmail.com>]

I know, I know, I Googled it and lots of people have had a similar
problem, but nowhere is there a satisfactory solution posted.

I have two frequently updated testing systems and I'm seeing this
problem on only one of them (both laptops, both typically connected
via wifi). On the one with the problem, after suspend the nm-applet
shows networking disabled, and enabling networking has no effect
(which to me suggests a permissions problem somewhere). 'sudo service
network-manager restart' works to restart networking and automatically
connect, so it's "solved" to that extent. It used to be, though, that
networking would, as one might expect, RESUME after suspend and that's
what it's still doing on the other machine. Although differently
configured, the two machines are, as of a moment ago, updated at the
same time.

My user is in the netdev group on both machines. Each has the same
PolicyKit rules file:

polkit.addRule(function(action, subject) {
  if (action.id == "org.freedesktop.NetworkManager.settings.modify.system" &&
        subject.local && subject.active &&
        (subject.isInGroup ("sudo") || subject.isInGroup ("netdev"))) {
    return polkit.Result.YES;
  }
});

which appears to do the right thing. It still seems to me to be most
likely some sort of permissions problem, but I cannot for the life of
me figure it out!

Any thoughts as to where I should look next?

Thanks
Patrick