Send message to all connected resources

Hi all, I am running ejabberd 16.01 with mod_carboncopy.
I want to make it so that all connected resources receive all messages no matter what.

This sort of seems to work, if I have 2 clients logged in (both sitting at resource priority 0) and a new message comes in, I receive the message on both clients. All good so far.

If I then reply from one of the clients client#1, the next incoming message will only be received by client#1 even thoguh both clients are still sitting at the same resource priority.

The desired outcome is that both client#1 and client#2 receive inbound messages despite which replied previously.

I am not sure what is causing this, can this behaviour be changed in any way?