Configuring Hosted Exchange 2003 - GAL Seperation

Hi Guys,
following on from my previous post asking for details on how to configure exchange 2003 for multiple clients, i have run through the very useful articles that were recommended (http://www.msexchange.org/tutorials/Shared_Hosting_Exchange_2003_Part1.html)
I now have everything working except the following:
1) When seperated user connects via OWA they are only able to see users in their GAL - so this is fine
2) When same user connects via https over RPC from outlook client with cached exchange turned off they are only able to see users in their GAL - so this is fine
3) When same user connects as per 2) but turns on cached exchange they are able to view ALL users\groups in the domain - this is a problem.

I have checked and rechecked all permissions on GAL, Address Lists, OAB and cannot see a problem. Authenticated users only have 'list' permission. I have even put deny permissions on lists but still they are able to view all users when running in cached exchange mode.

Help appreciated

thanks, Jason