Metadata for imported pictures

When a picture is added to a shared album, the picture seems to be stored with the date and time of sharing (not the date and time if exposure). The sorting within the shared album is therefore not chronological according time of exposure. Time of exposure does, however, seem to be stored within the picture, as it does appear above the picture when viewing it (by double clicking on it) in the Photos app. Nevertheless, only the date and time of sharing is transferred with the picture when it is imported from a shared album into the library. Hence it becomes impossible to sort the pictures in chronological order in the library after importing them from shared albums. Does anyone out there know how to solve this problem?