Compute head movement from speech function work not very well when no webcam installed.

no webcam installed,and use Compute head movement from speech function
whichever high or low value of Pose-to-Pose Movement setting ,
character head movement alway like Pose-to-Pose Movement 100% with 23.0,23.1
(even set to 0% still move like 100%).
but 22.4 22.5 work opposite,

whichever high or low value Pose-to-Pose Movement setting ,
character head movement alway like "Pose-to-Pose Movement" 0%.

is that bug ?how to fix it?