Hi,
Bug?
no, this is not a bug but intended.
In JoomGallery exist three image sizes: thumbnail, detail image and (optional) the original image.
If you delete the original image, it can no longer be displayed, logically or?
I personally would delete the original images only if there is no more space on the server.
But there is the possibility to show the detail image, instead of the original image.
The whole applies to calling up the Pop-up box from the category view.
See Category View >> General Settings >> Popup box original image
in the Configuration Manager.
PS: Copying files manually is generally not recommended.
Regards
MrMusic