Manual pro-ration for sickness in previous period

Can the system please be updated so when we select manual pro-ration when entering sickness for a previous period this isn't ignored by the system.

Currently when we select manual pro-ration the system still automatically pro rates the salary for the employee just because the sickness was in (or started in) the previous period.

If we select manual pro-ration there is a reason for this, the system should not be ignoring our selection.