Yes, I do have a site and all of these files are saved to that site. Tried deleting the _notes folder and trying it all again - DW recreated a new _notes folder but nothing changed.
I have bound my contact_us.php to the processing form (contact_sent.php) and, when the data entry is correct and validated, I can use that binding to display the relevant fields that have been posted from contact_us.php. When there's invalid data, the contact_us.php form displays the "validation show if" error messages so I assume binding to the validation page is working in some form (although there's no listing in the bindings panel)
As a test, I've created a completely new site and created a very simple form and vaildation page in it. Sadly the same happens; I can process the form data and, if valid, display the bound fileds from the original form in the processing page or, if validation fails, bounce back to the original form and display the "show if" errors based on validation failures.
Any more ideas?