I tested this with 6.2.6. I can't get "Use Ajax" to prevent submission/redirect on a simple form.
1. Enable default webform modules on simplytest.me
2. Create a webform on admin/structure/webform and configure it with a single radios element and configure settings to "Use Ajax"
3. Add a field to the "Basic page" content type that is a Webform reference
4. Create a basic page referring to the webform from step 2
5. Submit the webform on the basic page node and observe you are redirected to a standalone confirmation page at /node/1/webform/confirmation? (that is what I think is the bug, being redirected instead of staying on the page)
6. Similarly on /form/page-feedback the submission results in a full page refresh.
Active
6.2
Code
Help in slack pointed me to the Settings > Confirmation > Confirmation type which then has a message letting me know that only certain confirmation types are supported by Ajax.
Automatically closed - issue fixed for 2 weeks with no activity.