If the 302 status code is received in response to a request using the POST method, the user agent must not automatically redirect* the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.*
http://www.ietf.org/rfc/rfc1945.txt
IE does redirect automatically. So IE isn't doing it right either. Since nobody is doing it right, I'd pick the guys doing it wrong that make the most sense. What a surprise: that's not microsoft.