cart rule

[Saraaa]

Hello,

I have prestashop 1.6.1.23.

I have created some cart rules for my clients i choosed diffrent amounts and the same options for all the clients see in attached 

when the clients used the cart rules in their orders, something went wrong 

sometimes when the cart rule value is smaller than the total product price in the order detail, a second voucher is created containing the difrence between the discount amount and the the total product amount.

I have been testing since days, I can't understand how does it fuction.

Any help please.