20% off coupon giving irregular results

Cart has a 20% coupon set up. It applies to all products in a specific category, in this case "sale". Tested with several computers, several browsers. There have been many customer complaints. Client has tested extensively and gotten the same results as I have.

Some products accept coupon; others don't. Even with products that don't accept the coupon, if a second item is added to the cart, the coupon is being applied to the second item/third items automatically.

I created a second test coupon and got exactly the same results. I added a minimum $1 purchase level and still got it.

In the admin area, a look at the products listed, it only shows 30 or so of the 64 products, but that could just be a cut off on number of characters in that field. But specifically testing items from the showing 30 items in that list doesn't seem to be a factor. Some work, some don't.

Screen shots have been emailed to Ray. It is the same log in as in previous tickets; no changes. The test coupon is still active for testing.

This is the first time this client has done a percentage off.

Any assistance most appreciated.