Bruce,
The 302 occurs when moving from a non-secure page to a secure page, NOT on (failed attempt) postback. Here is the 302 error request and response.
Request:
GET /Documents.aspx HTTP/1.1
Accept: image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/x-silverlight, application/x-silverlight-2-b2, */*
Accept-Language: en-us
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; InfoPath.2; .NET CLR 3.0.04506.590; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)
UA-CPU: x86
Accept-Encoding: gzip, deflate
Host: netdatadesign.net
Connection: Keep-Alive
Cookie: .<Truncated>
Response:
HTTP/1.1 302 Found
Date: Mon, 15 Sep 2008 21:45:02 GMT
Server: Microsoft-IIS/6.0
X-Powered-By: ASP.NET
X-AspNet-Version: 2.0.50727
Content-Encoding: gzip
X-Snapsis-PageBlaster: v:2.3.0;c:-PC;x:-;r:-
Location: https://domain.net/Documents.aspx
Cache-Control: private
Content-Type: text/html; charset=UTF-8
Content-Length: 157
<html><head><title>Object moved</title></head><body>
<h2>Object moved to <a href="https://domain.net/Documents.aspx">here</a>.</h2>
</body></html>
TIA for your help.