w3.org won't serve DTD imbedded in Docbook generated output - butonly to IE

[Jon Leech <jon@alumni.caltech.edu>]

     We're having a weird problem with some content generated by Docbook, such as

http://www.opengl.org/sdk/docs/man/xhtml/glTexImage2D.xml

     At some time relatively recently, this has started failing with IE, although
it still works fine with Firefox. Our server admin has chased this down as far as
finding out that when

http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd

is fetched with an IE 7 User-Agent, it's rejected by www.w3.org with the following
resulting from the HTTP dialog:

HTTP/1.1 503 Go away
Date: Mon, 23 Feb 2009 13:32:48 GMT
Server: Apache/2
Content-Location: msie7.asis
Vary: negotiate,User-Agent
TCN: choice
Retry-After: 86400
Cache-Control: max-age=21600
Expires: Mon, 23 Feb 2009 19:32:48 GMT
P3P: policyref="http://www.w3.org/2001/05/P3P/p3p.xml";
Content-Length: 2
Connection: close
Content-Type: text/plain

     Looking at the P3P document referenced from this doesn't shown any
obvious reason for the error. I tried to figure out an appropriate W3C
mailing list to inquire on but there are dozens of them and nothing
springs out as being obviously relevant. Has anyone else run into this?
Any idea what's happening and how we might address it?

     Thanks,

     Jon Leech