IM inbuilt client - losing contacts

We have upgraded users to 7.0.1 client and this obviously comes with the inbuilt IM client. Some users are able to add contacts and after logging off/on the client keeps the contacts, others lose their contacts list and have to search again… I thought that this was stored server side and when you reconnected it pulled the config down. Am I wrong or is there a client setting somewhere that I have missed…

Any help gratefully received!

Dave