Subscribing (digest) to subfolder of a NetFolder

Subscribing (digest) to subfolder of a NetFolder gives back a notification for changes for the whole NetFolder.
Subscribing (email) to subfolder of a NetFolder gives only notifications for this subfolder and its elements, as expected.

Is this by design or just a bug? I'd like to have the ability to subscribe to a subfolder and get then only files and folders listed which are located in the specified folder instead of the whole NetFolder.

Regards,
Marco