ZipCart download reveals hidden items, Bug or Feature?

Hi!

The ZipCart download (and maybe other 'iterate'-type plugins like slideshow?) seem to reveal hidden items in albums.

I found out kind of by accident as after installing the plugin, i downloaded a full album which had exactly one hidden image in it.
After viewing through the downloaded material i noticed this image, as i hadn't seen it for a long time too.

But the pictures are 'hidden', thus not 'protected' by any means other than obscuring it's existence.
So is this really a -bug-?

I think a site-wide configuration option would do nice

Any ideas on this?