Special price not showing in cart

I've got a number of items on special in my store. The discounted price displays correctly on the product listing. However, when the items are added to the shopping cart it charges the full price.

The items affected are all priced by attributes. I checked the attribute set up, and "Apply Discounts Used by Product Special/Sale" is set to "Yes. Is there something else that I need to check?

Products which are not priced by attributes are fine - the special price shows correctly in the cart.

I am running v1.3.9h, and have the Stock By Attributes add on.

Many thanks!

Well I would contact the module developer "Stock By Attributes add on" and ask for his expertise ...

The key is to use Winmerge and compare the core file of Zen Cart with the add on's files to munge the code into the core file..
If the module was written for an earlier version of Zen is where you get into trouble..