There are 2 active network connections on the windows 8 machines: Network 3, of type Ethernet, and Bell, a dsl connection requiring username & password. When I connect to the Bell connection then the machine gets assigned a public IP address. Anyway, the Bell connection was of type Private Network, and the Network 3 was of type Public Network -- exactly the opposite of what they should have been. After changing those settings, everything started working as expected.
It was trivial to change the Network 3 connection to be private (Windows + I, click on Internet access, then View Connection Settings at the top, where I could Select Network 3 and turn on "Find Devices and Content"). Making Bell public was a little more involved, as it does not show up under View Connection Settings. So I had to Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\NetworkList\Profiles, find the profile with Profile Name Bell, and change its category to 'blank'0 (i.e., leave it blank). See more detailed instructions & screenshots.