NFS tcpwrapper - Strange issue

I encountered a strange issue with tcpwrapper (hosts.allow) and NFS yesterday and I am wondering if anyone has come across the same issue or knows if it is a bug.

The issue has to do with mountd and how to tcpwrap it. In the man page it states that you need to use rpc.mountd, so we have formatted our hosts.allow with the following:
rpc.mountd:10.xx.xxx.0/255.255.255.0 10.xx.xx.xxx

However when we do this it will work, but only for the first address/subnet range. As soon as we add another address we get the following error in the messages log:

rpc.mountd[2196]: connect from 10.xx.xx.xxx denied: request from unauthorized host

I have found that if we change the mountd entry to the following:

mountd:10.xx.xxx.0/255.255.255.0 10.xx.xx.xxx

All of the servers start working with out any problems.

Has anyone come across this issue?