OMG. I just wasted 2 hours staring at my screen with my eyes 6 inches from the screen saying to myself - p opened - p closed - div opened - div closed. Because I couldn't find the error. I was adding a div to my page and it fubared some margins. Finally I found it. It was this...

#home #main .column:nth-of-type(3) {

Apparently that does not mean class .column :nth-of-type. It means div:nth-of-type. I assumed it would only target the class. It does not - it targets the 3rd div. Maybe you already knew this. I did not.

I wonder if that applies to :last-child too? tested - yes it does.