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**
addons/purchase/models/purchase.py
'''
        This function returns an action that display existing picking orders of given purchase order ids.
        When only one found, show the picking immediately.
        '''
        action = self.env.ref('stock.action_picking_tree')
        result = action.read()[0]
        
        result.pop('id', None)
        result['context'] = {}
        pick_ids = sum([order.picking_ids.ids for order in self], [])
        
        if len(pick_ids) > 1:
            result['domain'] = "[('id','in',[" + ','.join(map(str, pick_ids)) + "])]"
        elif len(pick_ids) == 1:
            res = self.env.ref('stock.view_picking_form', False)
            result['views'] = [(res and res.id or False, 'form')]
            result['res_id'] = pick_ids and pick_ids[0] or False
        return result
    @api.multi
    def action_view_invoice(self):
        '''
        This function returns an action that display existing vendor bills of given purchase order ids.
        When only one found, show the vendor bill immediately.
        '''
        action = self.env.ref('account.action_invoice_tree2')
        result = action.read()[0]
        
        result['context'] = {'type': 'in_invoice', 'default_purchase_id': self.id}
        if not self.invoice_ids: