• What airplane and how fast are you going?

    In the airbus and boing planes in the descent mode it pitches for speed and the target speed automatically reduces as you extend flaps. This makes the aircraft pitch up slowly after you extended flaps... It just tries to slow down as per schedule.

    The copilot either flies manually or it usually uses the autopilot vertical speed mode. Here the autopilot pitch doesn't depend on the target airspeed directly.