Added VPN connection to RDP session settings, now RDP session attempts logon with wrong account

I recently modified an existing RDP Session entry in Remote Desktop Manager, setting it to connect a Microsoft VPN connection if unable to ping the server. Since adding the VPN connection info, this RDP Session is not using the specified credentials for the RDP connection. Instead, it seems to attempt logon using my windows user account, which doesn't have rights to RDP to the target computer. That logon fails, showing me the target computer's lock screen with an error message on it. If I click through the message, I can manually enter the correct username and password at that logon screen to successfully access the target machine.

The windows user account is also the account used to authenticate to the VPN connection, so I don't know whether the account info is coming from the VPN connection or the windows session that RDM is running in. Because the VPN connection uses certificate based auth, the VPN settings in that RDP session are very simple, as shown below.

Why is the the RDP session not using the credentials specified for the RDP Connection?