nfs shares question

A quick nfs question. First I run showmount -e on a machine:



/shared user1.mydomain.com



But then I run showmount -a on the same machine:



user1.mydomain.com:/shared

user2.mydomain.com:/shared

192.168.2.100:/shared



How is this difference possible? In the above example, showmount -e
shows that /shared has only been exported to one host, user1. Yet other
hosts have mounted it. I don't understand. Is this a result of some
network magic? Or is a program sitting on nfs, such as sfs? Thanks for
any help.