diff -r 973556094501 stock.py
--- a/trytond/trytond/modules/stock_lot/stock.py	Mon Oct 26 13:23:09 2015 +0100
+++ b/trytond/trytond/modules/stock_lot/stock.py	Mon Oct 26 13:45:41 2015 +0100
@@ -133,19 +133,17 @@
                     out_quantity = Uom.compute_qty(out_move.uom,
                         out_move.quantity, out_move.product.default_uom,
                         round=False)
+                    out_move_vals = {}
                     if quantity < out_quantity:
                         outgoing_moves.extend(Move.copy([out_move], default={
                                     'quantity': Uom.round(
                                         out_quantity - quantity,
                                         out_move.uom.rounding),
                                     }))
-                        Move.write([out_move], {
-                                'quantity': Uom.round(
-                                        quantity, out_move.uom.rounding),
-                                })
-                    Move.write([out_move], {
-                            'lot': move.lot.id,
-                            })
+                        out_move_vals['quantity'] = Uom.round(quantity,
+                            out_move.uom.rounding)
+                    out_move_vals['lot'] = move.lot.id
+                    Move.write([out_move], out_move_vals)
                     quantity -= out_quantity
                 assert quantity <= move.product.default_uom.rounding