The scourge of intermediate flap
Having flown the 737/2/3/4/5
The Boeings have lots of small flap increments to minimise the ballooning effect caused by most other aircraft when the wing area is increased for a given speed.
Since the Boeings I have flown the F50,Bae146 and A320/321. All of these aircraft "balloon" when the second stage of flap is selected.