I have had this happen one time in an FSO. I was in a Stuka, and my gear touched the top of the plane in front of me. I saw the dust trail from the wheel, and heat the impact. I managed to pull up just as I touched, so there was no damage.
Tried it again later to see if I could make it happen, and I passed right through the other plane.
Dont know how, or why it happened... but it hasnt happened since.