I don't particularly end sessions on a knocked bar, but it has nothing to do with what I think I'm training my dog and everything to do with my pride in getting it "right." It sounds like you identified the problem- throwing the ball a bit too early. I do the same thing, and when I do it, I make a mental note, run the sequence again, and don't make the same mistake.
That said- one of my fellow students in class has a dog that she cannot stop and start over again. This act will completely shut the dog down (he's a very soft min-pin). So if they make a mistake, she keeps running. For that dog, there is no correction ever. No abrupt stopping.
So I think to some extent it does depend on the dog.
C-ATCH Pimg - DOB: 2/06, RATO, UJJ (x2), DJA, HIT, CA, CGC, High in Games, Reserve High in Standard- CPE Nationals 2014
RATCHX High Jinks vom Neuanfang - DOB 9/12 (Gotchya Day: 1/23/2013) CA, agility superstar in training