When you first go from the hair room to the pose room the dynamics is set to zero for the hair. After you bend your character at the waist, select the hair and click the arrow next to the dynamics dial. In the menu that opens, click "Recalculate Dynamics." Then wait. But be carefull. I had the ponytail prop on a character and bent him at the waist then bent his head down further to see if the ponytail would hang straight down. After I clicked "recalculate dynamics" the danged ponytail flew right off the head and hung in the air about three feet away. Ha! Silly me!