special price not apply to group price(per item) mod

I'm using zen cart 1.3.8a with group price(per item)
once I set up a special price, only customers without assign to a group can get special price. any customers in groups, will get the group prices. the listing price is correct, but when add to cart, the price becomes to the group price, not the sale price. weird.
Does anyone has a solution for this issue？
Thanks in advance.

I have the same problem. Does anyone has a solution?