SP5: File Field: access to a selected but restricted file in a update engine clear the current restricted value

I have a john user (RWA) which access to a page with a box of type file. Previously, with root, I created a container pointing to a file only visible by root.

1) The Corpv2 templates display an empty line for my john user as the file is not available for him
2) If my John user update the container and enters the fiel field: an empty file field is displayed. Just by clicking on OK without selecting another file, remove the default value entered by the Root user (so it cancels the "hidden" file selection).

In such a case it would be great to have at least a warning message in the file field mentionning: "this content object is pointing to a restricted file: do you want to keep the current value or select another file" kind of message.