Grow multiselection widget to show all items if yexpand is not set
The multiselection widget for lot_requried field in product.template form doesn't have the yexpand attribute set to 1 and it doesn't show all the items (it shows an scroll) what makes easy to forget to mark some of the items.
But if you set the yexpand=1, it fills all the available space leaving lot of useless blank space inside the widget.
The best option is to use the required space to show all the items