Mail Scanner updating Ticket but not triggering Workflow

A customer is using the Mail Converter to update tickets. If I add myself as a Contact and create a ticket, I get the initial notification. If I reply to this email, when the Mail Converter runs it adds my email, as a comment, to the Ticket correctly. But what does not happen is the workflow notification to the user who is assigned to this ticket, i.e. they do not know when the ticket has been updated by the customer.

If I use any of the other triggers, such as changing the Description, then an email is sent as it supposed to be.