Hi zanderz,
Thanks for your message, and welcome to deSEC!
What you are observing is that our server redirects all http:// requests to https://. To avoid this (and to benefit from HTTPS security), you should be making update requests directly via HTTPS.
This can be achieved by adding ssl=yes
to the configuration (see Configuring your dynDNS Client — deSEC DNS API documentation).
Stay secure,
Peter