automatic modifier for service line is re-applied at fulfillment

Hi,

We are using automatic modifier that is applied for service lines.

User overrides the selling price resulted from the automatic modifier by using a manual modifier  ,

covered product is shipped.

service line is fulfilled, however, for some reason  the price is recalculated and the system does not obey to the manual price the user selected that overided the automatuc discount.

there is no reprice activity after the fulfillment.

any idea why it happens and how to prevent that except of asking the user to change the calculate price flag of the service line to Freeze which does not make sense.