[Exim] From header problem with switch to Maildir

We recently switched from mbox to Maildir format (courier-imap).
Everything is working well except some email clients are reading the
incorrect From line in the message header:

>From jhodge@??? Fri Dec 05 12:45:29 2003

Instead of:
From: Jeff Hodge <jhodge@???>

When a user tries to reply their email client then uses
jhodge@??? Fri Dec 05 12:45:29 2003 as the full email address.

This was not a problem when we were using uw-imap with mbox format. We
are using exim 3.36. Here is the local_delivery transport we are using:

local_delivery:
driver = appendfile
directory = /home/$local_part/Maildir/
delivery_date_add
envelope_to_add
return_path_add
maildir_format

Is the driver the problem? Any help would be appreciated.