Mine was a contract bug to explore Duna. Some how, according to the game, I flew a probe to Duna, entered the SOI, landed on the surface (using parachutes and a small engine to soft land), transmitted data from the surface but I did not enter the atmosphere even though I was floating down and gathered data on the way.
It only registered the atmospheric entry after I went into orbit and then into sub orbital. Originally I flew straight into the atmosphere and aerobraked. Not as elaborate as some of the others but a strange one.