Sending a message from the participants list when messaging is disabled sends email containing link to error page

We currently have messaging disabled at the site level.  

An instructor has gone to the participants list in a course and selected a couple of students (checked the box beside their names) then scrolled to the bottom of the page and selected from the pulldown "with selected users...Send a message".

The students are then sent an email containing the message from the instructor.

If messaging is turned off then should the instructor be able to message the students this way?  Is this expected behavior?

I have added a forum post https://moodle.org/mod/forum/user.php?id=1750527