"Layered navigation block" issue - active filters

[webbusiness23]

Hi,

 

i need the layered navigation block to keep all the characteristics active in the front office, and not hide some of them once a characteristic is selected. 

 

 

Let's assume i have 5 filters; if i check one of them, the other 4 disappear, because there are no products that have associated the selected characteristic. 

But further more, i need a product who has characteristic_1 AND characteristic_2, and this means that i need to have all of the active, so i can select further.

 

 

How can i do that?

(I'm using Prestashop 1.5.3.1)

 

Thank you!