Linq update in for each loop odd behaviour

In the attached code snippet I have a for each loop on a linq result set.

Each loop updates a LocalPrice field and then calls CalculateRowTotals which is a routine in the partial class of the order details linq entity.

CalculateRowTotal simply updates the totals in the row based on the new LocalPrice.

For some reason CalculateRowTotals does not write the totals back to the database... the LocalPrice is changed without issue... whats going on?
thanks
Wing

'Do we have a current order
        Dim ordHead = (From p In db.bb_order_headers
                 Where p.AccountNo_FK = c.AccountNo And p.OrderStatus = "N").SingleOrDefault

        If Not (ordHead Is Nothing) Then
            Dim ordDetails = From p In db.bb_order_details
                     Where p.OrderHeaderId_FK = ordHead.OrderHeaderId
                     Select p
            For Each rec As bb_order_detail In ordDetails
                'For some reason 
                rec.LocalPriceDB = c.GetLocalCurrencyPrice(rec.Price)
                rec.CalculateRowTotals()
            Next
            db.SubmitChanges()
        End If

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