COM port default to mission planner

I was connecting my quad running Revo FC to my PC Mission Planner via a pair of telem radio module. I don’t know what I did…the COM port in the drop down menu next to CONNECT defaults to “COMxx-255-MissionPlanner”, instead of “COMxx-Quadrotor”. After pressing CONNECT button, of course connection failed.

I am running Windows 10. Baud rate is set to 57600 for Mavlink. When using the same telem radio module to connect another Revo FC to the same PC works fine.

Can anyone shed some light on what has gone wrong. Thank you.