DA polishers are designed to do just that, the whole idea is that if you apply too much pressure the pad stops rotating preventing you from burning the paint.

Sounds like you pressing down too hard on the pad (I think it should rotate around once per second) but also if you are polishing you have the speed set too low too. I think its meant to be 4 - 5 for polishing?

Sometimes on level horizontal surfaces the weight of the machine is enough and you dont need to apply any more pressure.