IPs skipping relaydelay

Hi,

In the past week I've been experiencing IPs that are not being
challenged by relaydelay.  The usual practice is to tempfail an
IP for an hour after which if the sending e-mail server responds
correctly, the e-mail is delivered.  

The system on which greylisting is invoked is a redhat el4 system.

Most of the time this works.  But for a subnet starting with 216.83,
they are getting by the relay check.

Anyone have any ideas on this?

Philip