We just pushed up a fix for an issue where a coupon may be configured to apply to one category, but the discount applied is greater than the amount in that category. The discount would then spill over to products from other categories (that are not valid for that discount).
discount string: 1-80 configured for category DEFAULT.
$60 Product A from category DEFAULT
$20 Product B from category sale
$-80 is taken from Product A with $-20 left over... which makes Product B free.
Now, the discount in category DEFAULT is confined to that category only and the total is correctly shown as $20.
We try not to make changes to existing store versions, but in this case we believe the fix is constrained to this specific case. We're posting this notice just in case you notice anything strange with price-based coupon discounts.