Raw field can still be mapped to next table?

Hi, I believe this is a bug but perhaps intentional. 

When a field in the DSA is set to ‘Raw’ , you can still map it to the MDW. When you do this the field is not mapped (as it is impossible), however the table does become dirty (red). Then, when you refresh the instance, the field is actually added in the MDW, but not mapped. 

I attached a GIF that shows this.