It happens whatever it's from the camera, a screenshot. It happens as well when a picture is moved from an album to another. The same happens whatever in the Gallery or the Storage browsing mode. However, the data (EXIF:Modified, EXIF:Taken, File:Modified) are well shown in the details view of the images.
A restart of the App’ temporary fixes the problem.
I just installed* the last version as from 04/07 and the problem still.
Thank's Pierre for this new application
*Cleared autorisations, cleaned storage, uninstalled previous beta, installed new one.