4
When you're going through the wizard, do a view page source of the page that gives the problem when you leave it. There should be a hidden form field called 'op'. It should be set to 'checkDB'. Also check what the form action is set to, it should be index.php, which will call up the /install/index.php page again and do the check. All I can think is that the redirect is not working on your setup correctly, but it's strange that the rest of the wizard works as it does the same thing each time using a different 'op' value.
If these are all okay, I probably can't help any further.