The default behaviour is what you are seeing now. The server will only deliver the message to a single client with the highest priority. If there are multiple with the same highest priority, then the server determines which one to send it to, which I would guess is the last one to connect.
The other behaviour (which you want) requires the setting of the property defined in that thread so the message is delivered to all cllients with the same highest priority. If they are different prioirities, then only the highest one will get the message.
