Service Management Service Order Billing - Percentage covered doesn't allow zero

When overriding the Billable flag to  1  - for billable and changing the percentage covered to 0  , the percentage covered keeps reverting to 100% ,   you need to enter 0.1 or less in order to make the system calculate a billable amount .  This does not seem to be functioning correctly  ?     Is there something else that needs to change make the program accept 0%  ?

Secondly is there anyway to allow the entitlement check field to be changed either on the work order header or the parts list  or labor lines