After playing around with some settings in RouterOS in preparation for using pfsense as a hardware firewall. I now get persistent ipv6 DNS leaks from my Mikrotik router. I've unplugged the pfsense device and restored my RouterOS config file from before I started re-configuring. I've flushed DNS cache in RouterOS and on the client computer but I'm still getting ipv6 DNS leaks.

My RouterOS DNS is set to 4 different external static ipv4 addresses to override the ISP's DNS which is working. But I now get their equivalent ipv6 DNSes showing up too on the client computer even though they haven't been configured. This didn't happen before. How do I remedy this?

I do not want to use any ipv6 services except for when a client wants to connect to the internet trough their own VPN service.