different kde versions on NIS lan

We have an all 8.2 lan with clients running kde via nis and nfs from a central server. All OK under 8.2. but then I upgrade one client to 9.0 and login to my account from there. It works fine but then I can't login again from an 8.2 client. (it sits at the flashing globe forever). This defeats the idea of having nis. Apart from upgrading all boxes at the same time, is there any way around this? Indeed, should this happen at all? Thanks, Steve.