[imp] Compose Forward Preferences Missing

[cjdl01]

After updating to imp 5.0.16 from 5.0.15, it seems that all my users  
have lost the block on their preferences page to configure Forward  
preferences, and everyone is defaulting to "as attachment".

I haven't edited my preferences.php at all, neither have I created a  
preferences.local.php, so I can't think of anything I would have done  
to do this.

I have this block of code in my preferences.php:

// *** Compose Forward Preferences ***

$prefGroups['forward'] = array(
     'column' => _("Compose"),
     'label' => _("Message Forwards"),
     'desc' => _("Configure how you forward mail."),
     'members' => array('forward_default', 'forward_format')
);

// Should the body text of the original message be included?
// If this preference is locked, the user will not be able to select the
// forward method.
$_prefs['forward_default'] = array(
     'value' => 'attach',
     'advanced' => true,
     'type' => 'enum',
     'enum' => array(
         'attach' => _("As attachment"),
         'body' => _("In the body text"),
         'both' => _("As both body text and an attachment")
     ),
     'desc' => _("How should messages be forwarded by default?")
);

// When forwarding a message, should we use the same format as the
// original message (for the body text)?
$_prefs['forward_format'] = array(
     'value' => 0,
     'advanced' => true,
     'type' => 'checkbox',
     'desc' => _("When forwarding a message in the body text, should  
we use the same format as the original message?")
);


Now, I understand I can create a preferences.local.php, and change  
'value' => 'attach', to 'value' => 'body', but I think that will only  
affect the default behavior for new users, and not influence anything  
an existing user has configured.

Any idea why this block might be missing?  And how do I go about fixing this?

Thank you,

-Chris