Discount does not update when plus / minus buttons used

[Signalman]

I am using PS 1.5.6.1 with the default theme. Shop (not finished yet) is at shopDOTmartelldesignsDOTcoDOTuk.

 

We have a discout rule set up that takes £0.10 off of the cost if you have five items or more.

 

When you adjust the quantity on the cart page (index.php?controller=order), the number updates as does the sum for the total price but when you tip over the threshold, it does not use the revised price per unit and remove or add the discount (depending which way you go).

 

The screenshots attached show:

1. 4 items at £1.50 with no discount.

2. when the + is pressed, the qty and total price are updated (5 x 1.50 = 7.50), but the price per unit should be shown as 1.40.

3. same as 2 but after page refresh with correct unit price.

4. going the other way, pressing - button takes qty down to 4. Total sum is correct based on the wrong price (unit price should now be 1.50 and discount removed.

5. same as 4 after page refresh.

 

With the scenario set out in 2 and 4, when you go through the checkout process, the right value is eventually shown, so it there any way to get it to refresh the price for the discount rule.

 

If not, how can I remove the plus/minus buttons?

 

Peter