I am not sure if what I see is intended or not. Supposed you have a table in a database that is also a part of a diagram. If one deletes fields in the column view and then switches to the diagram view the fields that were deleted remain, in an italic font.
My expectation is that having deleted them from the column view they are no longer a part of the database schema and therefore should not appear in the diagram.
Not sure if this is a bug or a new feature that could be added )