Cannot specify server name that doesn't contains letters after "f"

On Windows 10 (and iPad), when adding / editing a server, if the domain does not contain any letters after "f" then it will not allow the settings to be saved.

I'm guessing it's assuming that the server name is an incomplete address in hex, but there's no address format that uses hex with decimal points.

 

Steps to reproduce:

Add a server, with the server name "cafe.ca"

Save button stays grayed out.