While in manual or tapshift mode it will likely act like this. The pcm will command downshifts based on throttle % and vehicle speed regardless of what manually selected gear you have, and the downshifts can be a bit harsh on the tapshift transmissions when the pcm has to do the work for you. If the car is in D range then it should never take off in 2nd gear from a dead stop and then as you accelerate from the stop drop back into 1st.