Error on shipping discount

[yourzed]

Hi, I have a prestashop 1.6 and I'm having random problems with the shipping discount. On almost every order it works well, but sometimes it fails and the order completes without the shipping price discount.

I have configured the products with weight.

I only have one shipping method, with zones and prices for the zones.

I have some buying rules, in specific the one that it fails is configured as this:

 

Free Shipping

Customer limit: none

From 01/01/2016 To 31/12/2016

Minimum amount: 39

taxes included, shipping excluded

total dispo: 555555

total dispo for customer: 555555

Restrictions: Country -> Spain

Actions:

Free shipping

Discount: none

 

With this config today entered an order

 

Customer country: spain

Product price without tax: 37.19

Product price with tax: 45

Total products: 45

Total Shipping: 3.45

Total Order: 48.45

 

As you can see, the rule failed to apply to this order.

 

But It worked for this one:

Customer country: spain

Product price without tax: 32.23

Product price with tax: 39

Total products: 39

Discount: -3.45

Total Shipping: 3.45

Total Order: 39

 

Can someone help me to find what is wrong? Thanks a lot