I'm trying to construct a product filter which allows to select multiple checkbox from the same field like

CATEGORIES
[ X ] Category 1
[ ] Category 2
[ X ] Category 4

I know that i can get it setting facet Operator to "OR" but:

First of all:
Operators options are not displayed in Facets admin configuration

I forced the code to show them, but when i check "OR" operator it seems as nothing change:

Filter continues working as always, when I click one checkbox, others dissapear and I cant select multiple values to get the correct products display.

I guess it's a commerce module modification, isn't it? Somebody can help me?

Thanks in advance and sorry for my english