In desperately searching for an answer I have used Firebug to lookat the headers and compare with my testing server. Not having any experience in this area my interpretations may be innacurate - maybe someone can interpret for me?
Testing Server:
Response Headers
Cache-Control no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Connection Keep-Alive
Content-Encoding gzip
Content-Length 20
Content-Type text/html
Date Mon, 24 Sep 2012 12:47:36 GMT
Expires Thu, 19 Nov 1981 08:52:00 GMT
Keep-Alive timeout=5, max=100
Location
http://192.168.72.11/modx/index.php?id=59&username=600678&email=bobd%40testdomain.com
Pragma no-cache
Server Apache/2.2.22 (Unix) PHP/5.3.10
Vary Accept-Encoding
X-Powered-By PHP/5.3.10
Production Server
Response Headers
Cache-Control no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Connection close
Content-Type text/html; charset=UTF-8
Date Mon, 24 Sep 2012 11:48:12 GMT
Expires Thu, 19 Nov 1981 08:52:00 GMT
Pragma no-cache
Server Apache
Transfer-Encoding chunked
X-Powered-By PHP/5.2.17
Perhaps not relevant to my problem, but why is Connection close on the production server and keep-alive on the testing server?