Designer does not support 2nd level schema inheritance

1. in a project enable WebUI
2. create schema schemaA
3. create document type FirstDocType
4. create document type SecondDocType that inherits from FirstDoc
5. create document type ThirdDocType that inherits from SecondDocType
6. switch to Designer
7. head over to UI / Layouts / Local Document Types
8. select FirstDocType
9. click metadata
10. click Configure
11. observe schemaA appears in the right panel (Catalog tab)
12. select SecondDocType
13. click metadata
14. click Configure
15. observe schemaA appears in the right panel (Catalog tab)
16. select ThirdDocType
17. click metadata
18. click Configure
19. observe schemaA is not present in the right panel

Expected behavior: the schema should be available
Note: this generates errors when using it because Designer does not know it.