Cart won't show quantity increase if the product has attributes

[sYs^]

When I add a product to the cart and then I try to increase the quantity of the product with the 'cart_quantity_up' or 'cart_quantity_down' button the 'cart_quantity_input' field won't update. This only happens if the product has attributes and it still updates the cart block on the right.

 

Example product: http://www.buderusbolt.hu/buderus/647-buderus-k-profil-22-600-1000-lapradiator.html

 

Running on Apache 2.2.16 with PHP 5.2.10 (with xcache) and MySQL 5.1.49. Server OS: Debian Squeeze (x64)

 

PrestaShop version 1.4.3

 

We had this bug on IE, FireFox and Chrome.

 

Thanks for any reply in forward and sorry for the Hungarian language in the shop.