Sorry, I was working from memory ... published items are distributed via the routing mechanism based on the affiliations list for the node. We are not using cluster tasks for this as I had alluded earlier.
To troubleshoot, you might take a look at the affiliation for the subscriber (client 1 in your case). Is the client subscribed using a full jid, or a bare jid? Also, there are various options for using presence-based subscriptions and access controls as well. Finally you will want to ensure that a published item is distributed to all connected subscribers, not just the highest priority session.