@stephenw10:
Something easy to overlook is the 'Disable Negate rules' option in System: Advanced: Firewall and NAT:
This is unchecked by default so it normally negates the specified gateway for a policy based route if the destination is a local network. It should apply in the case here. Do you have this checked?
Personally I always check this box because when I am deliberately separating local network segments I want to do so by simply not adding firewall rules rather than having to add block rules.
Steve
It is unchecked (default), wasn't even aware of it, maybe it's not working as intended in 2.1?