The way you have it currently set, you have two different settings but both are beyond the lease time. Due to both of these settings being different and beyond the lease time, is why you are getting inconsistencies, as I previously mentioned.
The 7 and 7 day intervals work hand in hand with a default DHCP lease time of 8 days. DHCP renewals are half the lease interval right, whcih is 4 days.
Once the lease is lost at the 7th day, then if you left scavenging set to default, it will clean out that old lease entry from DNS in all zones it existed in. My suggestion is at least that if you want to keep an aggressively short lease, to at least make the lease period 2 days and scavenging 1 day. If a laptop gets a record at 8am on a Monday, but unplugs and goes home and comes back on Thursday, the laptops will attempt to get the same lease. If you do not set these settings, and the scavenging period is more than the lease, unexpected results will occur.
Therefore with an 8 hour lease, the refresh time is at 4 hours. That needs to be taken into account with additional traffic, and how DNS updates, as well as how WINS handles it with the constant requests coming through. Otherwise, expect issues to occur.
The following, which goes into much more detail of what is actually occuring, was compiled and posted by Chris Dent in the Microsoft DNS newsgroup. Possibly to handle many laptops coming in and out of the network. So you would think a shorter lease time would work. Therefore, the client machine will asking for a refresh every four hours. It would seem reasonable to reconsider the DHCP Lease duration, 8 hours is, after all, extremely short. An A record is created as a dnsNode in AD.
Tombstoned record exists for value of the DsTombstoneInterval attribute, which is 7 days by default. The DnsNode object is moved to the Deleted Objects for the length of time of the tombstoneLifetime attribute value. The Active Directory Tombstone Lifetime is listed in the schema. This value does not change after upgrading all domain controllers to newer Windows versions or by changing the Domain or Forest Functional Levels. The entry in the schema. Therefore, this will tell you what the value is depending on what Windows operating system was used to install the very first domain controller in your infrastructure: The values can be changed.
Please read the following for information on how to change it: The directory size should level out eventually, when you reach the point where the number of tombstoned records being flushed is equal to the number being created. DHCP uses pings for conflict detection. Enable address conflict detection.