This is arising from the convenience of single press setup, isn't it? Powerline should still have passwords and such to stop two unrelated networks from connect

This is arising from the convenience of single press setup, isn't it? Powerline should still have passwords and such to stop two unrelated networks from connecting, so it's more that the default settings are a little too hands-off. I've found the firmware on TP-Link is a bit lacking. For a while they had a rogue DHCP server on their newer connectors that couldn't be switched off, until the most recent firmware update. This would cause all sorts of issues with that device.