iFreiight Lines are not getting taxed when imported through Interface even though taxable fiield val

When loading Interface invoices into the interface screens, even if you Place a value of Y in the taxable field and a Tax Code in the tax field, after import the tax code does not appear in the Invoice screen (and of course the Freight line does not get taxed).Item Lines work fine but Freight lines are not getting taxed after they come throough the Interface table?Is there a setup that needs to be turned on to make this happen or is it not possible when Interfacing Invoices?Thanks