When using DOpus 8, if I copied files from one directory to another, replacing an existing file of the same name, DOpus would keep that existing file's "Date Modified" value and apply it to the incoming file.
I've tried, and tried, but cannot get DOpus 9 to do this. It always keeps the date modified of the copied file.
Maybe it will do it if you turn off Prefs - File Operations - Copying Files: Preserve the timestamps of copied files.
I don't think Opus, with any combination of options, has ever explicitly set the timestamp on the copied file to that of the replaced file, but it's possible that happens in some situations due to a feature of the filesystem so maybe that's what you saw in the past. If that's the case then the option to preserve the timestamps of copied files would definitely undo what you want to happen.