C6900 Cable Modem with custom DNS settings not passed on to DHCP network clients

I have further diagnosed the problem, and here's some more details: 

• When parental controls are enabled, the router does *not* pass its configured DNS servers to clients (either those obtaining DNS servers automatically or those configured with the gateway router's IP address as its static DNS server). Instead, it passes the ISP's automatically detected DNS servers to clients. This is viewable in the client's DNS settings after an IP address is acquired, and from performing an nslookup from the client -- it uses the ISPs DNS servers, not the configured servers on the router. That is an outright bug. 
• When parental controls are disabled, and the router has configured custom DNS servers, it *does* pass the configured IPv4 DNS servers to clients (either those obtaining DNS servers automatically or those configured with the gateway router's IP address as its static DNS server). However, it *also* passes IPv6 DNS servers which are automatically acquired from the ISP to those same clients, and when a domain name is resolved, the IPv6 servers from the ISP are used, not the IPv4 DNS servers configured on the router. I have not found a way to either turn IPv6 off on the router, or to configure custom IPv6 DNS server addresses. This appears to be another bug. 

The use case here is simple: if you configure the gateway router to use custom DNS servers instead of the DNS servers obtained automatically from the ISP, clients obtaining DNS settings automatically from the gateway router should perform their lookups against the custom DNS servers, not against the ISPs DNS servers. 

I'd classify these bugs as major (or severe, whatever) as they result in a network-wide loss of intended functionality. This loss of functionality prevents easy problem resolution if the ISP's DNS servers go down and you need to point clients elsewhere, or using other DNS servers for performance or filtering reasons. Netgear's Parent Controls are very limited and don't appear to completely work (but that's an entirely separate conversation -- I tested that for hours too), and so using a separate third party filter is a comon need. (ironically, going direct to OpenDNS rather than through the router's configuration seems a better option). But unfortunately, the router's behavior prevents this.

The only resolution I can find to solve this (barring some answer / fix from Netgear), is to run a completely separate DNS server, and point clients at it instead, which is completely redundant and unnecessary -- the router should handle this simple behavior.