Recertifying users in USA

I have a group of servers in the UK, and a few in the US.Servers are connected by a VPN.

All servers and users are in the same domain, but in different OUs (USA and UK).

When I recertify a USA user, who’s mailfile is on the US server, the recertification process never seems to work.

The names.nsf record on the UK server updates with the new certificate, but this never seems to replicate over to the USA server. However, updates in other record information, e.g. phone number, do replicate accross for the same users.

I am at a loss as to what is failing, and how to update the remote certificates. I don’t want to start copying and pasting between replicas of records if it can be avoided.

Does anyone have any ideas?

Thanks

p.s. If I RENAME the users, the update replicates across to the USA no problems. This just seems to be an issue with recertifications. FYI: We are not running a CA