That is completely normal, the transmission adapts to how you are driving based on the performance driving programing (PAS). In other words, it determines how you are driving and adjust itself accordingly.
When operated in Sport Shift mode, the transmission will delay upshifts and allow earlier downshifts. In addition, the transmission can sense enthusiastic driving, at which point it may delay upshifting and downshift earlier when braking. This is designed to maximize vehicle performance.