This is caused by the super power jump, if you jump in the air onto a vehicle, it will make it fly into the sky, or likely explode.
To fix this, turn off your superpowers by using the following cheats: nosupermove and nosuperpowers
I think those are correct, anyway, this will stop you from flinging cars around, as your character will move the same as they would in SR3 or some SR4 missions.