I was tending to a gang attack at the northernmost hideout in the Downtown area. I was doing so with an M4 and I was shooting people off their bikes as soon as they came around the corners. Apparently the game engine missed the fact that I shot one of the duos off of their bike, cause they flew off, but the bike kept driving. No one was on it. The game knew this because it was hitting things and doing flips and driving off again and then coming back and flipping and driving off again. Once the attack ended I investigated it. I got run over trying to get on it. Shot it and it kept going. Finally it cornered itself into a building so I got on it. No carjack animation. Just hopped right on.
Ghost carjackings, and now ghost cars. Hmm.