Yes, Explorer does it in a weird way. It changes quality and also adds an Adobe XMP tag. I think, compression level is hardcoded here like in MsPaint.
This issue has been duscussed by Seven Gurus
on this forum and elsewhere
. IMHO, the best advice is to avoid using Explorer for changing attributes.
To change date in a photo properly, I would recommend a free program called XnView
(Minimal version would do).
It allows to change date without problems (menu Tools - Change timestamp). And you can change date for multiple pictures at a time!