sales price not shown in cart for products with attributes

Hi! My site was running all well and good, except that the salesmaker price doesn't show up in shopping cart. They still show on the product description pages, but not in shopping cart. Therefore, customer will still have to pay full price instead of sales price during checkout.

This seems to happen only for products with attributes. For example, in my store, the laptop Dell 600m doesn't have attributes set up, then it shows after-sales price (see here) . While the laptop sony fs730/w, which does have two attributes to be chosen from, then shopping cart only shows pre-sales price (see here).

What's going on? How can I fix this problem? Anyone, please help! Thanks so much!