diff --git a/modules/purchase_trade/lot.py b/modules/purchase_trade/lot.py
index ab48007..1492f5f 100755
--- a/modules/purchase_trade/lot.py
+++ b/modules/purchase_trade/lot.py
@@ -4233,7 +4233,7 @@ class LotUnship(Wizard):
                 lot = Lot(r.id)
                 if lqt and r.r_lot_type == 'virtual':
                     shipment = None
-                    qt = lqt.lot_quantity
+                    qt = Decimal(str(lqt.lot_quantity or 0))
                     mode = 'both'
                     if not lqt.lot_p:
                         lot = lqt.lot_s
@@ -4246,13 +4246,17 @@ class LotUnship(Wizard):
                         shipment = lqt.lot_shipment_internal
                     elif lqt.lot_shipment_out:
                         shipment = lqt.lot_shipment_out
-                    #Decrease forecasted virtual part shipped
-                    lot.updateVirtualPart(-qt,lqt.lot_shipment_origin,lqt.lot_s,mode)
-                    #Increase forecasted virtual part non shipped
-                    if lqt.is_planned_transport():
-                        LotQt.restore_planned_open_quantity(lqt, qt)
-                    elif not lot.updateVirtualPart(qt,None,lqt.lot_s,mode):
-                        lot.createVirtualPart(qt,None,lqt.lot_s,mode)
+                    if not shipment:
+                        continue
+                    # Restore the selected scheduled quantity only once, then
+                    # remove its shipment-linked lot.qt so it cannot be
+                    # unlinked again from the shipment planned tab.
+                    if qt:
+                        if lqt.is_planned_transport():
+                            LotQt.restore_planned_open_quantity(lqt, qt)
+                        elif not lot.updateVirtualPart(qt,None,lqt.lot_s,mode):
+                            lot.createVirtualPart(qt,None,lqt.lot_s,mode)
+                    LotQt.delete([lqt])
                     if lqt.lot_p and lqt.lot_p.line:
                         affected_lines.append(lqt.lot_p.line)
                     if lqt.lot_s and lqt.lot_s.sale_line:
diff --git a/modules/purchase_trade/tests/test_module.py b/modules/purchase_trade/tests/test_module.py
index d6fc592..35c5e33 100644
--- a/modules/purchase_trade/tests/test_module.py
+++ b/modules/purchase_trade/tests/test_module.py
@@ -704,6 +704,9 @@ class PurchaseTradeTestCase(ModuleTestCase):
             lot_quantity=Decimal('40'),
             lot_p=lot,
             lot_s=sale_lot,
+            lot_shipment_in=Mock(),
+            lot_shipment_internal=None,
+            lot_shipment_out=None,
             lot_shipment_origin='stock.shipment.in,12',
         )
         lqt.is_planned_transport.return_value = True
@@ -722,14 +725,53 @@ class PurchaseTradeTestCase(ModuleTestCase):
             state = wizard.transition_start()
 
         self.assertEqual(state, 'end')
-        lot.updateVirtualPart.assert_called_once_with(
-            Decimal('-40'), 'stock.shipment.in,12', sale_lot, 'both')
+        lot.updateVirtualPart.assert_not_called()
         LotQt.restore_planned_open_quantity.assert_called_once_with(
             lqt, Decimal('40'))
+        LotQt.delete.assert_called_once_with([lqt])
         lot.createVirtualPart.assert_not_called()
         Lot.assert_lines_quantity_consistency.assert_called_once_with([
             purchase_line, sale_line])
 
+    def test_lot_unship_deletes_zero_scheduled_lotqt_without_restore(self):
+        'unlinking a residual zero scheduled lot.qt only cleans the shipment tab'
+        wizard = lot_module.LotUnship()
+        wizard.records = [Mock(id=10000007, r_lot_type='virtual')]
+        purchase_line = Mock()
+        sale_line = Mock()
+        lot = Mock(line=purchase_line)
+        sale_lot = Mock(sale_line=sale_line)
+        lqt = Mock(
+            lot_quantity=Decimal('0'),
+            lot_p=lot,
+            lot_s=sale_lot,
+            lot_shipment_in=Mock(),
+            lot_shipment_internal=None,
+            lot_shipment_out=None,
+        )
+        lqt.is_planned_transport.return_value = True
+        Lot = Mock()
+        Lot.return_value = Mock()
+        Lot.skip_quantity_consistency.return_value.__enter__ = Mock()
+        Lot.skip_quantity_consistency.return_value.__exit__ = Mock()
+        LotQt = Mock()
+        LotQt.return_value = lqt
+        Move = Mock()
+
+        pool = Mock()
+        pool.get.side_effect = [Lot, LotQt, Move]
+        with patch('trytond.modules.purchase_trade.lot.Pool',
+                return_value=pool):
+            state = wizard.transition_start()
+
+        self.assertEqual(state, 'end')
+        LotQt.restore_planned_open_quantity.assert_not_called()
+        lot.updateVirtualPart.assert_not_called()
+        lot.createVirtualPart.assert_not_called()
+        LotQt.delete.assert_called_once_with([lqt])
+        Lot.assert_lines_quantity_consistency.assert_called_once_with([
+            purchase_line, sale_line])
+
     def test_add_physical_lots_requires_linked_transport(self):
         'physical lots can only be added from a scheduled quantity'
         LotQt = Pool().get('lot.qt')