Actually 10.6.5 has "fixed" that resolver issues -- now OS X
always prefers IPv4 over IPv6 when both A and AAAA responses are received, except in edge cases where one of the responses takes an abnormally long time to be returned. There's a difference of opinion on whether the 10.6.5 change is good or bad, as early adopters and those experimenting with IPv6 will see it as a flaw while the bulk of the Internet at large presently sees it as a good thing due to sites becoming unreachable due to botched IPv6 configurations -- the same reason that Google refuses to hand out its AAAA records to DNS servers that haven't specifically been approved for "Google over IPv6" (as HE has).
As to the original question, the autoconf in my ifconfig output was an error as I was actually pasting two pieces together -- I've been using a combination of a tunnelled connection and an automatic 6to4 gateway via my Time Capsule, since I can't configure the HE 6in4 tunnel through that (seems a manual 6in4 configuration doesn't work when using a PPPoE connection

). At any rate, in my case OS X seems to handle rtadvd just fine as long as I'm configuring manually, regardless of whether I script it through ifconfig or use the System Preferences. I think the key is the
net.inet6.ip6.accept_rtadv setting, which I leave OFF (0) for the HE tunnel machine, and I've noticed that setting up my IPv6 configuration manually in System Preferences actually toggles that setting off automatically as part of the process. I suspect when rtadvd starts up it may be looping back the link-local assignment to the local RA listener, which causes the default route to get updated inadvertently. Obviously running rtadvd and listening for RA's would be mutually exclusive in most cases.