Dealing with deleted addresses in shipping configuration form

1. Go to an investigation's Shipping tab and edit the shipping configuration.
2. Create and select a shipping address and save.
3. Go to the Addresses page.
4. Delete the newly created address.
5. Go back to the investigation's Shipping tab => the default shipping address still appears even though it no longer exists. (Should this be the case? Should we show a warning instead?)
6. Edit the shipping configuration => the default shipping address' drop-down menu is blank because the address no longer exists. (Fortunately, the form cannot be submitted until an address that exists is selected.)

I think we need to handle this use case a bit more clearly, somehow.