The issue of line items missing is complex and as far as we are aware it is fixed in 6.1.5. Alec was a massive help.  The issue we think came around low stock items in the basket. Say you have 3 items in your basket. Two have plenty of stock and one is the last one. If the stock level is reduced to zero when the order is placed (transferred to payment). If the customer users the browser back button it could screw things up as technically the item is now out of stock.  If the stock chan