Hello Rob,
Thank you for your message.
Actually, this is expected behavior. Notice the 'Automatically generate Host password' checkbox selected on the second screenshot. If it's selected, you instruct the program to generate the password for you (i.e. it will be unique for each instance of a Host installed) rather than let you set it manually.
That is, if you want to set the same single password for all instances of your installed Hosts, you should deselect that checkbox and this will unlock the single password authentication option in the configuration settings.
Hope that helps.