Document type inheritance: Can't see or edit fields from super type

To reproduce (in Go Green):

• Go to the "Configuration", and add a document type with supertype "Document"

Expected: Supertype fields can be seen
Actual: Can't see supertype fields

• Go to the documents and create a document of the newly created type

Expected: I can add a Title (which is in the supertype)
Actual: I can't add a Title

• Save

Expected: The document is saved
Actual: The document can't be saved, because there is a field in the supertype which is required (which I can't edit)