Forms :: Values Populated From A Subform To A Main Form Not Saving To Table?

I am having a problem with calculated fields that are populated on the main form from the subform not saving to the table the main form is linked to.

I created a Purchase Order table that has information on what emplyee created the record, reason for order, customer information if its ordered for a customer, creation date, eta date and notes while the Purchase Order details table is for information on the supplier, product item number, product name, quantity and cost. they are linked by the Purchase Order number which is the primary key in the Purchase order table. it all looked good so i made the form with the Purchase Order Detail as the subform, i got the form all working great and how i wanted it but then i decided i wanted the supplier name and the subtotal of the cost in the main form populated or calculated by the values in the subform.

I copied the fields i wanted populated in the main form to the subform footer and added the calculation for the subtotal then added the formula to the source code on those fields in the main form so the values would populate. it all worked great on the form and the values populated as they were supposed to so i saved the record and went to look at the tables and i found that while the values in the calculated fields that I populated from the subform showed up in the form they didnt save to the table while the non calculated fields saved fine. i did some experimenting and found that if i delete the code and put the data source back to the table in the form and just type something in the text box it would save to the table but not if i had the code in and let it populate.

an example of one of the codes i used to populate the data in the main form is:

=[frmNewPurchaseOrderDetails subform2].[Form]![txtsubfrmSupplierID]

did i mess up in the code or did i do something to the relationship between the form and the table?