The Airplane ends up in the water.
This has been discussed many times, and it happens if your joystick is not properly calibrated, or if you have another device which present itself as a joystick that has been assigned to the Slew axis.
The sudden movement because of the lack of calibration is causing the airplane to very quickly move away from the editor, which cannot keep up and give the error, which means the airport disappeared (not really, it was the airplane which slewed away because of the uncalibrated joystick ) while you were editing it.
Other than calibrating the joystick, it's better fixed by removing all joystick axes from the Slew events.