If you sign in as 'test' with password 'test' you can see the browser is displaying all the form data in the address box after submit. I didn't have this problem at one time, but then I made some changes to the script (I thought unrelated changes) and now the form info shows up.
Another side affect is file uploads. I've got another form in the site that allows the user to upload files. They won't work unless the filename is sent using the POST method.