I HAVE seen the sunken ship icon you described.
I think there is an issue with the spawning of aircraft in formations of 2 or more.
One one campaing i was playing with external camera on, i will hit the period key and cycle through contacts to see how serious a threat is on the other end of the radar detection line. much to my surprise i see one aircraft climbing out, then another aircraft next to him (his wingman) splashing into the sea. then at this point the grey sunken ship icon appears there.
__________________
|