Oscommerce, elavon, and discount codes - help!

Online store successfully running oscommerce with Elavon as the merchant account. Last week, the owner decided she wanted to offer free shipping with an order of 6 or more products.

There are many great discount code modules that work fine.

In all of our tests, everything was great. Now the customer can go order 6 and get a discount of $19.70. The customer gets a correct receipt. In our admin section, the order is correct. However, at Elavon, the orders are processing with the discount amount ADDED, rather than subtracted.

I have emailed support at Elavon… they say the programming must be wrong. I can’t find anything wrong and, as I said, everything looks right on our end. I have asked the developer of the module. He passes the buck (and rightly so, I think) to the merchant processor.

Anyone have any experience with this? For the moment, I went into the shipping module and changed the actual shipping amounts, so the total is correct, but it doesn’t show the shipping charge as a discount, which the owner would like.

Any help is greatly appreciated!