A patch has been submitted in nginx-devel maillist, please review. After the fix, the test result is:
telnet 2001:250:1800:1::88
Trying 2001:250:1800:1::88...
Connected to 2001:250:1800:1::88.
Escape character is '^]'.
GET / HTTP/1.0
Host: [2001:250:1800:1::88]
HTTP/1.1 200 OK
Server: nginx/1.1.1
Date: Wed, 24 Aug 2011 12:26:00 GMT
Content-Type: application/octet-stream
Content-Length: 0
Connection: close
MYHEADER: [2001:250:1800:1::88]