I'm unable to add a Upstream DNS Server

[dmshimself]

Whn I specify an upstream DNS server spec and press save, the server I've set stays on the screen momentarily and the
"Only ever query DNS servers configured below" radio buton is turned on, but the server I added isn't displayed. I've reshresfed the screen a couple of times and tried a couple of times. I've searched the dnsmasq.conf files and those in the dnsmasq.d directory but the server isn't to be found (by me at least!)

In my case I want to add
/lan/10.13.100.210

but I get the same effect if I simply try and use
10.13.100.210

If I manually put a
server=/lan/10.13.100.210

into dnsmasq.conf and restart dnsmasq, then all is well and I get the result I'm after

Am I using the GUI the right way?