"LAN default route" option does not work

Since upgrading to 4.26.7, the node serving the LAN I have a laptop connected to has started handing out a default route to itself. I used to disable this by disabling the "WAN". I want it to advertise only a route to 10.0.0.0/8 like before. I have "LAN default route" disabled but it doesn't seem to have any effect, even after rebooting the node. How do I stop the node advertising a default route this in 4.X? 

This is default behavior by dnsmasq as far as I can tell. I can work around this by edit /etc/dnsmasq.conf  and adding "dhcp-option=3". Obviously that's likely to be overwritten by the next upgrade or configuration change.