DDNS update to wrong zone

[John Hascall]

We are seeing a weird issue where DHCP (3.0.1)
starts using the wrong zone for DDNS updates
after a rejection.

Our DHCP server has update rights to various
subdomains but not our main domain.  Occasionally
somebody enters a 'bogus' name which (rightfully)
gets a refusal from the DNS server, but then
later queries will also use the maon domain zone.

Example:

     aname.subdomain.iastate.edu (zone subdomain.iastate.edu) = OK
     badname.iastate.edu (zone iastate.edu) = REFUSED (as expected)
     another.other.iastate.edu (zone iastate.edu) = REFUSED (why this zone!)
[but updates to any subdomain.iastate.edu which was updated before
 the refusal still seem to work]

Is this a known issue that was fixed in a later release?
Or which anyone else has seen?

Thanks,
John