You'r right
After further testing The same was happening to 'Contact Us'
The only thing that was added to both the AAQ and CU was the Zen non CAPTURE mod.
This must be the culprit
Before I deleted the 400 error page as the redirection, selecting the back button of either AAQ or CU directed the user to the 'No page found'. Then oddly enough when selecting the back button again of the 'Page Not found' the user is returned to the original and correct web page.
Thanx
mike