Question on cost calculation

Hi,

today I have tested activity cost feature by input some value in an activity, after save it seem that the total cost for parent activities and project cost have change correctly. If I change the value of activity cost all cost values are also update correctly except when I input 0 in the activity cost the cost on parent activities and project are not update. So if I want to change all cost values to zero I have to manually edit every cost values (parent activities and project cost).

Is this an intention?
(Projector V8.1.6)

Thank you.