yes, but the error saying "Unknown folder" is triggered in get_floder (call: https://github.com/Nicofuma/phpbb/blob/ticket/11480/phpBB/includes/ucp/ucp_pm.php#L333) and this block is in view_message (call: https://github.com/Nicofuma/phpbb/blob/ticket/11480/phpBB/includes/ucp/ucp_pm.php#L399) and it's too late, the wrong message was already triggered.