[imp] Filtering triggers auto-purge? A bug?

[Mariusz Czyz]

My setup:

Horde (horde)  3.1.4
Mail (imp)  H3 (4.1.4)

WebServer (Web frontend + MySQL backend) <--> IMAP email server

// should we move messages to a trash folder instead of just marking
// them as deleted?
$_prefs['use_trash'] = array(
     'value' => 0,
     'locked' => true,
     'shared' => false,
     'type' => 'checkbox',
     'desc' => _("When deleting messages, move them to your Trash  
folder instead of marking them as deleted?"));

// hide deleted
$_prefs['delhide'] = array(
     'value' => 0,
     'locked' => true,
     'shared' => false,
     'type' => 'implicit');

If an existing Filter Rule is triggered on a message in the Inbox the  
action of filtering will remove any messages marked as deleted. They  
don't get moved to the Trash, they just disappear without triggering  
the manual Purge action.

Is that a normal behavior or is it a bug?