That’s cracked it… so instead of adding in the proxies after the creation I created them in the initial configuration for the instance create and that’s solved the problem…
I am guessing that the LXD RESTAPI is fine with the lxd-client programs but has some edge conditions with direct access in this case via pylxd.
I’ll see when I can get time I’ll create a pylxd script that demonstrates this issue and raise an issue…