dnsmasq pushing static route over DHCP

Hello all,

I have a machine running dnsmasq to provide DNS and DHCP services to my 
small network. All machines are running FreeBSD 13-stable as of a week 
ago. Dnsmasq is installed from the port and is version 2.87.

I use DHCP options to push the default route to the clients. The 
relevant bit of my dnamasq.conf is:

dhcp-authoritative
dhcp-range=igb0,XXX.2.73.10,XXX.2.73.99,255.255.255.128,12h
dhcp-option=option:router,XXX.2.73.1

That all works correctly.

# route get default
   route to: default
destination: default
       mask: default
    gateway: XXX.2.73.1

Now I would also like to push a static route to clients to give them 
access to another network which is connected via OpenVPN. I've added the 
DHCP option 121:

dhcp-option=option:classless-static-route,XXX.3.73.0/24,XXX.2.73.2

That adds the new static route correctly. But it breaks the default route.

# route get XXX.3.73.1
   route to: XXX.3.73.1
destination: XXX.3.73.0
       mask: 255.255.255.0
    gateway: XXX.2.73.2

# route get default
route: route has not been found

I've tried just "option:static-route" instead (option 33). But that 
doesn't appear to work at all.

Can somebody please give me some clues. I'll happily admit that I don't 
know what I'm doing!

Thanks in advance.

Graham