Display post in columns problem

Hi,

I'm trying to use "Display post in columns" in archives and pages.
When I active this option, it works just sometimes. The first time I used it, It worked, but 1 minute later, I was modifying other things and suddenly this options didnt work... is selected but you can see just 1 column although you have selected 2 columns. You can see just 1 column but occupies only half of the total width... is very weird.

pd: can i write here in spanish?? thanks!!