Why can't I add IP Addresses to VPN Split-Tunneling settings?

Even with "Allow access to devices on local networks" enabled in General settings, I can't connect to either my printer or my AVR. Only after disabling the VPN do I gain access again.

Attempting to access printer or AVR settings by entering their respective IP addresses into the Split-tunneling textbox yields a "url is not valid" response.

To that effect, I don't believe the "Allow access to devices on local networks" to work effectively.

Any suggestions??