Yet another attribute stock level updating question

[kc_davis]

I am selling an item that comes in 2 sizes. I added this product and said it was in stock with a quantity of 40. I added a product attribute 'Size' and and checked the "Track Stock?" checkbox. I then added 2 values . . small and large. I then added these 2 attribute values to my item. Then I went ckicked on the products 'Stock" button to add stock values for each attribute value (20 small and 20 large).

I've done several test orders with the COD and credit card payment modules When the item is purchased the item quantity is correctly reduced but when I check the attribute stock levels by clicking on the stock button nothing has changed.

Now I've scoured the forums and it seems like I''ve got things setup properly . . but apparently not. In the admin console
in the Configuration/Stock section:
Checkstocklevel = true
Subtract stock = true

Any Ideas as to what is missing . . what else there is that I need to do to get this to work? . . help!