When a DHCP server is added to the Dns Update Proxy group, its records aren't secured, meaning that other DHCP servers can update the records.In additon, hosts can change the records and then become the owner of the record.When either type of client (static or DHCP client) initiates an A record update with its authoritative DNS server, it will first start by performing an SOA query for the FQDN of the client in question: The client then receives a response from the authoritative DNS server containing information about the server that is to process the dynamic update.From there, the client continues communicating with the primary DNS server that accepted the A record update.
This can occur with non-Windows machines that may not be able to request dynamic updates.
Just let it ride until you're seeing id 2501 events in the DNS Server event logs.
I'm afraid that you're going to have to approach this from the client end.
That doesn't exactly seem to be the case from your experience, but might be close.... Massimo, are you able to pull a wireshark trace and check the DHCPREQUEST Packet?
There should be a flag set to "1" if the client is supposed to update both the A record and PTR record.