If the notifyusers handler parameter is explicitely set to true as "notifyusers=true" then it is discarded and notification emails are not sent to users.
I believe the reason is how the value of this parameter is converted to a boolean value: using Boolean.getBoolean() instead of Boolean.valueOf()

Other cases work fine:

If it is not specified, emails are sent (as default behaviour).
If set to false, emails are not sent.