I am attempting to create a custom product details page for a project.  After I created the new page type (using PageTypeBuilder) and page template, I deployed it to my environment.  But, I am unable to select it in the "Commerce Settings" tab.  Every time I do, the "Save Successful" message is displayed, but the "Product detail page type" combo box is cleared out.

However, I can change the existing "[Commerce] Product page" to use my newly-created page template for display and I am able to select it in the "Product detail page type" combo box successfully.

Are you required to use a particular page type when creating a new, custom Product Detail page?  Is this configurable?