"Notes can also be bent by a heavy draw."

In the thread "Technique: Piano Accordion for The Recycled Muso" linked above is some discussion on this about (piano) accordion reeds - normally they only do this (with the 'traditional' design of PAs) if there is something out of adjustment with most piano accordions, but there is now a manufacturer who will modify instruments with a different reed and chamber mounting, which is designed to allow the reeds to be bent easily and intentionally (there was some discussion of the theory at their site), and there is a 2 stop positions on the keyboard to allow normal or bent playing styles.