Mixed experience with copy&save action of an 'Do-Not-Forward' email on outlook client

Recently, I encounter a case where some user (recipient) is unable to copy & save (e.g. ctrl+c & ctrl+v) an email with 'Do-Not-Forward/DNF' encryption enabled to a machine's desktop, while some can do so with same outlook client version use.

Known: An email with 'DNF' cannot be print, forward or copy content.

Seeking advice: What can cause(s) a DNF email (msg file) cannot be copy & save on desktop by the recipient?