I recently looked over out DNS server settings, and I found out that more than one DNS server (DC in our case) was scavenging records.
In order to put that right, I made a small script that makes sure that only the PDC is scavenging records:

 $scavengeInterval = 7
Get-ADDomainController -fi * | %{
 $config = gwmi MicrosoftDNS_Server -Namespace 'root\microsoftdns' -comp $_.name
 if($_.OperationMasterRoles -contains 'PDCEmulator') {$config.ScavengingInterval = $scavengeInterval}
 else {$config.ScavengingInterval = 0}