I noticed this as well, you saved me creating a thread about it. I was wondering why some people were suggesting hostname.local because from the code this clearly does not work on Duet Ethernet, the code to handle mDNS is specific to the Duet Wifi.
Not a big issue but with the soon-to-be-released 1.19 firmware the IP address will change for those using DHCP. If mDNS was supported then this would have been transparent (not trying to complain, I work in software and I understand you can't fix everything at once!).
Cheers,
Ben.