Tax calculation on a taxable inventory item calcultes both the input vat and outputvat

am having that issue when calculating tax. I set up my Tax upto rules and its actually working but after attaching the Vat Input and VAT ouput tax on the item in inventory its calculating both the taxs while making a purchase order and i only wanted it to calculate the input vat on PO and output vat on the sales order of the same item

this is what am facing