User A uploads a Microsoft Office document file to a NAS shared folder. The file owner is User A. User B then opens the file using Microsoft Office, edits it and saves the changes. The owner of the file is now User B.
The files ownership changes because of how Microsoft Office handles saving Office documents. When User B presses “Save”, Microsoft Office writes the modified document to a temporary file, deletes the original, and then renames the temporary file, giving it the same name as the original file. Due to this behavior, the owner of the edited file is now User B.