Grid system not working as expected (not working)

I don't know if I am doing something wrong, but the first time I try to use the "grid" functionality, I am not getting the desired results.

I have 3 test posts.
I have set 4 columns (and tried with 3), having the "Calculate width automatically" option checked.

I had for example inline style "width: 25%". The content is with correspondent width but it is not "inlining" with the other posts, so I have them stacked, with 75% of the view unused.

I saw other tickets and saw images of perfectly working grid.

If I'm missing something, maybe there is some UI design problem.

I haven't tried another theme.