In 5.4.2, when you make a new reply to someone, it defaults to previewing your reply irregardless of what is in your profile or the confing.inc.php file. Around line 39 of newreply.php you have this code:
if (!$Preview) {
$Preview = $config[preview];
}
Change it to:

if (!$Preview) {
$Preview = $config[Preview];
}
Seems to work ok for me.