Default Gateway/Route still created when metric set to 0

On the Settings/NetworkSettings page, on the line to set the IPv4 default gateway, next to the metric field, it says "optional metric (lowest is preferred, 0 is no default gateway)". 

I have two configured interfaces, eth0 and eth2.


But for some reason, it wants to set the default route on eth2, even with the metric field set to 0:

I have tried setting the metric on eth0 to 1:

But then I get two default routes with the wrong one first:

I cannot figure out a way to suppress the creation of a default route on eth2  I can only set it to a higher metric.  However this reduces, but doesn't eliminate the possibility of traffic going out the wrong interface (a potential security concern).