Adding mixins to new document types not reflected in CND

1. Create a new document type using the configuration editor in the CMS.
2. Check some of the checkboxes to add mixin types to the document type in the first step of the wizard.
3. Add some fields and commit the document type.
4. In the CMS console, export the CND. The CND shows the new document type as expected, but not the mixins.