Bug or enhancement: incoming email replies to cases don't execute user event script

I'm trying to write a user event script ("edit" event) to run after-submit when someone replies to a case email (either the submitter, assignee or escalatee).  However, despite NetSuite documentation that implies that this should work since it is an edit event, my user event script isn't triggered.  (I need this functionality to catch specific command strings in email replies from support engineers that will allow them to grab, comment on, or close cases by email.  I already have the code written to recognize the strings and do the actions, but it never gets the opportunity to run!) 

Support has agreed that it doesn't work and they think it was never supposed to.  So, Netsuite has called this an enhancement (number 138358) which hasn't gotten any votes because the headline on the enhancement was mangled so that nobody recognizes what it's for.