Child site WSUS not synching correctly

I have a child site that isn't syncing updates/update lists correctly from the parent site. On the parent site I have 5 update lists but only one of these is reaching the the child site. If I also look in the deployment package on the server there is 870 updates but on the child only 797.

When I initiate a sync form the parent all seems well. Checking the event viewer gives me the following logs suggesting everything is ok:-

On 9/28/2009 8:33:25 PM, component SMS_WSUS_SYNC_MANAGER on computer HKG-SYSCTR01 reported:   SMS WSUS Synchronization started.

On 9/28/2009 8:33:26 PM, component SMS_WSUS_SYNC_MANAGER on computer HKG-SYSCTR01 reported:   SMS WSUS Synchronization in progress. Current phase: Synchronizing WSUS Server.

On 9/28/2009 8:33:35 PM, component SMS_WSUS_SYNC_MANAGER on computer HKG-SYSCTR01 reported:   SMS WSUS Synchronization done.

There are no errors in the WSUSCtrl.log, wsyncmgr.log or WCM.log on the child site either. I also have another child site that is syncing fully and is set up exactly the same.

Is there anything I should be looking for? Why would some updates get synced and not others? This has really got me stumped. If anyone could shed some light i'd be extremely appreciative.