If you have IP/voip phones in the environment and you use DHCP vendor options to create vendor class and push the options.
If you use dhcputil to change the options values of the vendor class.
Or If you delete the class vendor class and re-create it again.
You notice that on the DHCP server service restart the old option values re-appear and the changes have been lost.
When you delete the DHCP vendor class using any of the methods:
1. UI using dhcpmgmt.msc
2. using netsh to delete the class.
The dhcp server only deletes the in-memory copy of the option values of the vendor class. However, it does not delete from the dhcp database.
Here are few methods to solve the issue.
1. Restart the DHCP server service in order to synchronize in-memory data with the database.
2. Delete all the option values
3. Delete the options
4. Delete the class
5. Restart the DHCP server service
6. Create the vendor class with new option and option values.
This issue is already fixed in Windows Server 2012.