I just hard deleted 3 pictures of my album and now they are gone, however if I go to ACP -> Applications -> Attachment browser this is what I get:
As you can see it looks like two files were successfully deleted however one of them appear to still be there, at least its thumbnail.
Clicking on any of the 3 images gives the following error message: "This attachment cannot be shown at this time. Please try back later."
I don't know if this is normal.