Formula Field not syncing back second time

We have one formula field in Dynamics which is doing the sum of demographic and behavior score field and then setting the final sum into total score field. This total score is formula field in Dynamics. When I am creating a new lead from Marketo then this field is working perfect and sync the total score back to Marketo but when I am sending updated score back to dynamic then this field doing the calculation and setting the updated score in total score field but the updated value is not syncing back to Marketo.