Impacted versions:
* 11.0

Steps to reproduce:
* Create company A
* Create company B
* Admin user with both companies but currently in company B
* Create Demo user only with company B
* Create fiscal position A to company A
* Create fiscal position B to company B
* Create vendor with fiscal position A with company A and the same vendor with fiscal position B in company B
* Create product and add the vendor created before
* Set like **Create a draft purchase order**
* Logging with Demo user
* Create sale order with one sale order line with route **make to order**
* Validate sale order

Current behavior:
The purchase order created by sale order has the fiscal position **company A**

Expected behavior:
The purchase order must have fiscal position **company B**
uom_id=self.product_id.uom_po_id)
        taxes = self.product_id.supplier_taxes_id
        fpos = po.fiscal_position_id
        taxes_id = fpos.map_tax(taxes) if fpos else taxes
        if taxes_id:
            taxes_id = taxes_id.filtered(lambda x: x.company_id.id == self.company_id.id)
        price_unit = self.env['account.tax']._fix_tax_included_price_company(seller.price, self.product_id.supplier_taxes_id, taxes_id, self.company_id) if seller else 0.0
        if price_unit and seller and po.currency_id and seller.currency_id != po.currency_id:
            price_unit = seller.currency_id.compute(price_unit, po.currency_id)
        product_lang = self.product_id.with_context({
            'lang': supplier.name.lang,
            'partner_id': supplier.name.id,
        })
        name = product_lang.display_name
        if product_lang.description_purchase:
            name += '\n' + product_lang.description_purchase
        date_planned = self.env['purchase.order.line']._get_date_planned(seller, po=po).strftime(DEFAULT_SERVER_DATETIME_FORMAT)
        return {
            'name': name,
            'product_qty': procurement_uom_po_qty,
            'product_id': self.product_id.id,
            'product_uom': self.product_id.uom_po_id.id,
            'price_unit': price_unit,
            'date_planned': date_planned,
            'taxes_id': [(6, 0, taxes_id.ids)],
            'procurement_ids': [(4, self.id)],
            'order_id': po.id,
        }
    @api.multi
    def _prepare_purchase_order(self, partner):