Wrong autoconfigured IPv6 address

This question is related to Windows 7, so I'm not sure if it applies to
Windows Vista.

I have an OpenBSD 4.4-current box at home that is configured to send
IPv6 Router Advertisements (by means of the rtadvd daemon). My Mac OS X
and Linux machines configure their IPv6 addresses using the prefix from
the Router Advertisements plus part of their NIC MAC addresses. However,
Windows 7 seems not to use the NIC MAC address but some bits I can't
figure out where they come from. My machine has three IPv6 adddresses:
link-local, IPv6 and Temporary IPv6. Looks like Windows 7 is using IPv6
privacy extensions, but what's even more surprising is that even the
link-local IPv6 address does not contain any single bit from the NIC MAC
address (it ends in :1494 where as the NIC MAC address ends in AA-E1).
In the NIC properties, inside the IPv6 settings, I can't seem to find
anything relevant. Another data point, which might be meaningless, is
that the NIC is a Wireless LAN adapter: Atheros AR5008X (yes, you
guessed right, this machine is a MacBook Pro).

Are you familiar with IPv6 autoconfiguration in Windows 7 (or Windows
Vista)?

Thanks in advance.