Why can't I create a new version of a photo edited in an external application, without Aperture making a new copy of the newly created Tiff?

When Aperture creates a new version from a RAW file, no new master file is created. This makes total sense and I understand why.

When I edit a photo in an external editor (Photoshop CS6) from within Aperture, Aperture creates a Tiff file to edit in Photoshop and saves it along with the RAW original once I have finished editing it in Photoshop. I understand why this is necessary too. So far so good.

But if I then ask Aperture to create a new version from the newly created image edited via Photoshop, it creates another new Tiff. I can't see why this is necessary. Aperture should be able to apply further new Aperture edits to the newly created Tiff in the same way that it creates new versions from a RAW file without duplicating the master - by remembering any new 'recipe' changes applied to the Tiff. It only needs to remember the edits made as the Tiff already now exists.

Can I stop it creating repeat Tiff files each time I create a new version from the Photoshoped photos?

Thanks in anticipation.