Parent post selector in a form that creates a repeatable field group is not being updated after Ajax submission

Symptoms

If you have a form that creates a repeatable field group and uses AJAX submission and it also has a parent post selector you can configure the parent selector field to accept a URL parameter as a preset value when the form loads.

This works fine when the form loads for the first time. The problem is that the field value in it is not populated to the field after the initial form submission.

Workaround