Yeah, I know. I had three emtpy ones. 
It worked after I removed the option that food should be stored in the stockpile. Therefore I know it wasn't working with the stockpile.
see:

Yes I know, the other ones cannot be filled, because there is no path. But the screenshot is after I removed the food from the stockpiles. Before that I didn't even had the walls.

It worked after I removed the option that food should be stored in the stockpile. Therefore I know it wasn't working with the stockpile.
see:

Yes I know, the other ones cannot be filled, because there is no path. But the screenshot is after I removed the food from the stockpiles. Before that I didn't even had the walls.