Steps to reproduce:

1. Clean installation of Ibexa DXP.
2. Add custom layout:

   ezplatform_page_fieldtype:
       layouts:
           sidebar:
               identifier: sidebar
               name: Right sidebar
               description: Main section with sidebar on the right
               thumbnail: /assets/images/layouts/sidebar.png
               template: layouts/sidebar.html.twig
               zones:
                   first:
                       name: First zone
                   second:
                       name: Second zone
   

3. Create new Content Type with the ezlandingpage fieldtype and disable the "Default layout" in the field type form (only custom layout should be enabled).
4. Try to create new content of the Content Type from the step above.

Result:
Default layout is chosen even if disabled.

The layout of this landing page is no longer available and you cannot publish it. Please select a different layout.

Expected result:
First available layout should be selected.