Problems with DHCPDECLINE with no IP Conflicts

I am running ISC's dhcp v 3.0.2 for a statically assigned dhcp
configuration. I have a php-mysql interface that I use to build the
dhcpd config file and restart the dhcpd process. Host MAC addresses
are assigned addresses with the fixed address directive in dhcpd.conf.
I am running into a lot of DHCPDECLINE entries in the log files. Hosts
are continuously rejecting and re-requesting addresses.

Upon changing addresses, the hosts appear to be fine, but some end up
with the same problem after a few days. Upon checking for ARP entries
after changing the addresses, I don't see another MAC using the
address, and the ARP entry will remain with the proper user's MAC until
it times out and is automatically flushed by our border router.

I first suspected that the problem was being causesd by
/var/db/dhcpd.leases being empty, but then after researching I found
that fixed address assignments are not stored in the leases file, which
makes sense. I understand that DHCPDECLINE messages originate from the
host thinking the address is already in use.. What would cause this?

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