You see, if your wall thickness is bigger or equal to half of the box size, there is nothing inside and so it crashes. This only happens with hollow boxes. Just tick 'solid' and you can make even 1x1x1 boxes.
ha, i no this is an old post, but i realized wat you mean. The wall size is for TWO walls per box, so they get too big like you said. I am enlightened, probably becos i am 14 naow.OH YEAH!!
Once I was sad, and I stopped being sad and was awesome instead.
True story.