??? This map apparently has some surprises even for me LOL.
I hadn't as yet enabled a remote allied strip as the custom P-40 object hasn't been redone yet. You may have hit one of the reserve Axis strips that had been set to the wrong field.
If you hit the enabled one I would think the protect objects setting would have prevented you from destroying the planes, but maybe there is a glitch, sort of uncharted waters here.
Or maybe I built one I forgot about LOL.