NIS group problem on NFS mount on HP client

[C3P Systems]

I have a hpux 11.0 client nfs mounting a directory from hp server.
As I exceeded the max limit for the number of entry's for a single group, I have created a second line for the same group id using a sligthly different name. but same group id eg:
fred:*:12345:joe,bill
fred2:*:12345:mike, greg
However if bill tries to cd to the nfs mounted directory which has the permissions of 750 with gid of 12345. He gets permission denied. The only way around this is to issue the newgrp command and then cd. Has anyone seen this.
BTW: the group file is NIS'd.