It's been in for years but I am just now getting around to automating the backups properly :-)
Yes, I can always open the web interface from this instance of SAD tool.
I have concluded this is just a bug in the management software. I ran a packet capture and whilst doing a backup, it only ever attempts to connect to port 44000. If I change the web listening port in the system connection from the correct value of 8443 to the default of 443, it attempts connections on 443 [and 80] whilst running a backup. Change it back to 8443 and it doesn't.