The thread with most of the information about this (linked in an older post above) has been restored so you can read it again:
https://resource.dopus.com/t/date-modified-changes-on-eml-files-when-hovering/10544
(The summary remains the same: It's a bug in a Microsoft component that dates back at least 12 years now and affects lots of software. You can disable the component as a workaround if the timestamps are more important than the information it provides.)