I've been playing with Fiddler 2and one of the entries looks suspect. I have pasted the raw data below and you can see that the Location header has not been rewritten. I'm not sure if this is the reason, but it is suspect.
I have also saved all of the sessions for this issue in the following Fiddler2 export if it helps:
Your help is greatly appreciated.
Also. To answer your PS. That was a typo on my part. I meant to write %.
HTTP/1.1 303 See Other
Date: Sat, 24 Sep 2011 05:14:21 GMT
Date: Sat, 24 Sep 2011 05:14:17 GMT
Cache-Control: post-check=0, pre-check=0,no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Content-Type: text/html; charset=utf-8
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Last-Modified: Sat, 24 Sep 2011 05:14:17 GMT
P3P: CP="NON COR CURa ADMa OUR NOR UNI COM NAV STA"
Via: 1.1 192.168.1.4 (IIRF v2.1)