I figured out a kludge work-around.
Select the profile to extrude and enter the Twist Angle and finally select the path. The solid is extruded as a right hand thread (positive Twist Angle) independent of what was entered.
Then using the Inspector window, select the solid just created. Change the Twist Angle from positive to negative and apply.
The solid will modify so that it is now a left hand thread.
It would appear the Twist Angle in the menu bar at the time of creation does not work properly. The one in the Inspector Box does work, but just take more time as it is a multi-step operation. Unfortunately, it means I will have to redo all of my work.