I think what's going on is that packets from www.ietf.org don't make it back to my ISP. A ping6 or traceroute6 doesn't show any ICMP errors and TCP sessions don't connect so it's not a PMTUD problem. So it's an actual timeout.
I also just started noticing this, that is, that it does not work. And there is a very simple explanation for this: 6bone space.
We (OCCAID) had recently turned up peering with a few networks (including HE and others) and as a result our outbound path to HEAnet and other networks had changed. Some of the abrupt route changes are being corrected today evening and hopefully should resolve pMTU problems in reaching www.ietf.org. If you continue to experience trouble in reaching thru OCCAID via IPv6, please don't hesitate to drop me a line in private. Regards, James