When creating a warning, the option to send a conversation doesn't check if the title is set. If it isn't set (but the message and checkbox are), the warning is issued and the conversation silently fails to be created.
Code:
$conversationInput = $this->_input->filter(array(
'conversation_title' => XenForo_Input::STRING,
'conversation_message' => XenForo_Input::STRING,
'conversation_locked' => XenForo_Input::UINT,
'open_invite' => XenForo_Input::UINT,
));
if ($conversationInput['conversation_title'] && $conversationInput['conversation_message'])
{
...
}