[Mimedefang] Problem with action_bounce Call

[Fox, Randy]

It's taken some time to narrow this issue to a specific issue, but I've finally found it.  I have the following segment in filter_begin:

    # ALWAYS drop messages with suspicious chars in headers or body
    # The following was changed from discard to bounce
        if ($SuspiciousCharsInHeaders) {
            return action_bounce("Message discarded because of suspicious characters in headers.\n");
        }

The example filter returns action_discard but I've elected to return action_bounce instead in an attempt to inform a potential sender why the message didn't make it to the sender.  The problem is, the text isn't included and all they get is a 5.7.1 550 reject and no explanation.  Is there a problem in the way I'm calling action_bounce that I'm overlooking?  I'm content with the generic 5.7.1 and 550 codes but I'd like the optional text to be included.

Thanks,
Randy