I'm fairly certain (dunno what the official rules are, but from what I've seen at comps) referees give you leeway for that. If you're in the middle of taking someone down and they jump the its not counted against you as its outside your control. At least, I've been dropped from singles before and jumped to try and get as good a position as I could out of it and my opponents weren't DQ'd. Slamming from the stand up is only a foul if someone jumps and the receiver very blatantly comes down hard on top. You have to make an effort still though. I've forced people down hard for doing it and been fine, probably because I did it with my arms while technically trying to do the correct counter but not caring if it hurt him or not. Its more like if I jumped on you and you essentially came off your feet trying to drive a shoulder in or something. I should add that on the other side of it even if its a contrived rule I don't think its a bad one, and I'm on the side of people who think it shouldn't be removed.