I have not been around to respond to my ticket.
Please see attached screen grab of server behaviour for my form checkbox.
When viewing the server behaviour form, the code for this element seems to have split itself across the 'Check If' and 'Equal to' fields'.
1. Select 'New Server Behaviour > Webassist > Validation
2. Set validation type; Required
3. Validation variable; ((isset($_POST["AcceptTerms"]))?$_POST["AcceptTerms"]:"")
4. Select the text associated with checkbox to apply my server behaviour to
5. Select Server Behaviour > Webassist > Validation > Validation Show If
6. Select Validation Fail; as created in 3, click OK
7. Double click the server behaviour for 'Dynamic Checkbox'
8. Form opens to reveal the code captured in attached image
9. With form open, I reapply the Validated item <?php echo(ValidatedField("newreg_501","AcceptTerms")) ?> from the dynamic data list.
10. Remove the code <?php "AcceptTerms")),1 ?> and replace with a '1' in the 'Equal To' field.
11. Click OK
12. Save page
13. Reopen the checkboxes server behaviour again.
14. Changes were not made.
I'm assuming this is not expected behaviour. I have no ideas if this is causing my initial issue.