Windows 8.1 gets IP from DHCP but remembers old DNS, how to fix?

Question

Domain Name System

DHCP server - isc-dhcp-server on Ubuntu Server, properly issues IP addresses. Previously issued 1 DNS - 8.8.8.8
All Windows 8.1 clients received IP addresses and DNS 8.8.8.8
Then I changed the config on the server so that DHCP issues two DNS - 10.0.1.1 and 8.8.4.4
Some clients began to receive new DNS, and some remained with one 8.8.8.8, if you turn off / on the interface several times, then the client receives both new DNS, and the next day in the morning after turning it on, he again has one 8.8.8.8. But this does not appear on all clients, and sometimes it suddenly appears, although the client has been working with new DNS for several days.
There are no other DHCPs on the network. The fact that sometimes the client still gets the correct DNS makes me think that Windows somewhere stores a record from the old DNS uses it and does not send a request to the DHCP server for a new one.

Answer 1

Thanks for answers. There was time to sort out the problem, it turned out it was in the server itself. The server issued either dns from the old config, then dns from the new one.
Despite the /etc/init.d/isc-dhcp-server restart command , the
processes were like this:

ps aux | grep dhcp
dhcpd     1186  0.0  0.0  19996  2164 ?        Ss   Sep22   2:01 dhcpd -user dhcpd -group dhcpd -f -q -4 -pf /run/dhcp-server/dhcpd.pid -cf /etc/dhcp/dhcpd.conf
root     26557  0.0  0.1  13648  5940 ?        Ss   15:52   0:00 /usr/sbin/dhcpd -q -cf /etc/dhcp/dhcpd.conf -pf /var/run/dhcpd.pid
root     26717  0.0  0.0  11748   920 pts/2    S+   15:55   0:00 grep --color=auto dhcp

dhcpd was launched on September 22, then the config was with the old dns, why it ignored the restart command is not yet clear.
nmap helped a lot:
nmap --script broadcast-dhcp-discover -p67 10.0.1.1
I saw that the dhcp server outputs data either from the old config or from the new one. I have not yet understood how this can be, but after killing the old dhcpd process, he created a new one himself and everything began to work as it should.

Answer 2

There are no other DHCPs on the network.

Sure? Try to access the DHCP server from the client computer (ipconfig /release, ipconfig /renew), while observing the traffic in wireshark. See if there are any differences in the server responses.

Answer 3

GPO?
Try to look in the registry for this particular ip address that is issued.