Custom Fields and Packages

If I take a custom field and assign it to , for example, the top listing package, then on the submission page this field is not shown for the lower listing packages.

This is great and how I would expect it to be.

However I need the ability to have fields not appear on any listing package. These fields would only be available for our admin to adjust from the listing post edit form. The owner of the listing does not need to see these internal fields.

Here is my issue. When I create a custom field and assign it to no listing package, I had expected it to not show up on the submission form for any listing package.
Instead assigning the custom field to no package makes the field appear on every listing package.

For me assigning a custom field to no listing package in order for it to not appear on any submission form would be perfect.