child products quantity change bug

[Giladd]

hello,

i have a problem which i think is a bug.... on child products only, when trying to change the quantity of the products from 1 to 2 it's go from 1 to 3 and then 5 and so on...
on regular products i don't have this problem.

here is a link to products with child object:
http://buycycle.co.il/bicycle-apparel-shoes/bicycle-socks/comfit-socks-white-buycycle

please advice.

[Milbo]

Maybe you use a quantity step for your child?