[squid-users] dns failover failing with 3.4.7

[Mike]

Running into an issue, using the squid.conf entry
dns_nameservers 72.x.x.x 72.x.y.y

These are different servers (under our control) for the purpose of 
filtering than listed in resolv.conf (which are out of our control, used 
for server IP routing by upstream host).

The problem we found like this weekend is if the primary listed dns 
server is unavailable, squid fails to use the secondary listed server. 
Instead it displays the "unable to connect" type messages with all 
websites.

How do we fix this so if primary fails it goes to secondary (and 
possibly tertiary)?

Thanks in advance
Mike