With op_fallback set to false, and assuming a group called "foo":

Chatsuite determines if a player is a member of group "foo" by checking the permission nodes chatsuite.groups.foo and group.foo. chatsuite.groups.foo is registered by chatsuite and defaulted to false; group.foo is not, and the default for an unknown permission is that it returns true for ops. Thus ops will appear to be in group foo unless the group.foo permission is explicitly negated.