I don't really have enough information to be able to answer this question. But I suspect if the global discount is working off the list or retail price in stock control, and your WINTER14 item has no list or retail price, the calculation can't be performed correctly.
Maybe discount first, then add the WINTER14 code afterwards. Or a more efficient way to do what you're doing would be to create a new customer account, perhaps call it CASH10. Set the account up identically to CASH, but on the Settings tab set the Discount Formula to: X-10% where "X" is your price to discount. (This would typically be the price field A-H depending on how the software was originally set-up.)
That way every time you invoice CASH10 sales, the 10% discount is calculated automatically. No need to spend time running the global transaction discount utility.