I ve got a question regarding a recently shooted RNP approach. The FAF was at 2000ft with a descend point being prior at around 3200ft...we had a max speed at IF of 185 kt. I used SPD intervention already there...passing the IF which was still some miles ahead of the descend point the aircraft started to descend I guess to the next step down altitude...is it because I pressed SPD intervention already at the IF before VNaV was in approach mode? How I avoid this and have the aircraft descending at the descend point...this of course is only a matter when the FAF lies after th descend point. Thanks