[sudo-users] Sudo and Group Changes

[Todd C. Miller]

This is not a problem with sudo.  When a user logs in their group
ids are set based on the passwd and group databases.  These are
stored in the kernel as part of the process's u (user) area.  Changing
the group file after the fact does not revoke the group for running
processes, it will only change the mapping of group id to group
name.

 - todd