Unsupported field can be saved with incorrect value in case the document type was changed.

Scenario:

1. Open document type in document type editor.
2. Add an unsupported required field e.g. required source field.
3. Open the document in Visual Editor.
4. Change some field

Expected: Save button is disabled and message in the top clarifies the situation. The link in the message allows navigation to a content perspective to fix the document.

Current result: the user can save and publish invalid content.

Note that the same is fair if to any supported field the unsupported validator was added. If a document had invalid content it will be saved and published with invalid field after adding validator. Content perspective prevents that behavior.