strange osx privacy address behavior

[Matt Ryanczak]

I've been troubleshooting a problem with some (not all!) OSX Lion
machines failing to connect to hosts outside of the local network when
using privacy extensions. I was wondering if anyone else has seen this
problem before.

Details:

OSX 10.7.4 (or 10.7.3)

privacy extensions are enabled:
sysctl -A net.inet6.ip6.use_tempaddr
net.inet6.ip6.use_tempaddr: 1

The machine is able to pings its local default gw. The eui-64 address is
used when this is done. This seems to be "normal" on osx.

The machine is not able to ping any hosts outside of its subnet when
privacy extensions are enabled. tcpdump on localhost shows that the
privacy address is being used.

Looking on the network via a mirror port I see the router (Cisco) doing
neighbor solicitations for the macs privacy address but I never see
neighbor advertisement in response from the mac. Also the router does
not show the privacy address from the mac in it neighbors table.

If I disable privacy extensions on the mac everything starts working as
one would expect.

For giggles I rebuilt one of these macs with a fresh install of Lion. It
worked for about an hour and then stopped working...

I have three macs behaving this way (two 13" mbp, one 15" mbp) and
another dozen or so (13" mba, 13"|15" mbp) that work fine with privacy
extensions enabled. Has anyone ever seen something like this before?

Thanks in advance!

~Matt