DHCP-INFORM and domain-name-servers problem

[Sébastien CRAMATTE]

Hello

We are woriking for a small ISP in spain. This ISP

Their internet bandwith provider assign them   2  different   /22 
subnet (1024 Ips).
Each  subnet has is own  gateway, dns, ...

Since few days  some of their customers can't  surf  ...

The DHCP server assign an IP, Gateway and DNS fron  one of ISPs to
windows client
But few hours later some windows client has changed their DNS server 
automaticaly  without change IP or gateway ...
Just the DNS servers ...

Windows client make some kind of DHCP-ACK and DHCPD answer with bad DNS ...
Seems that is known bug of DHCP-INFORM ...

We are running DHCPD 3.0.2
I haven't found any workaround or patch ...

Any help,clue or ideas are welcome

Regards