Today, I was deconstructing some foundations. I knew that my inventory was getting rather full, but I though that I would be able to complete before it filled up. I carried on, and as I was getting to the last 2 foundations, I ran out of space. Before I noticed the box for the second to last foundation, I deconstructed another foundation, which was mostly underground save for the tip of it. I was not able to find the box anywhere which leads me to beleive that it ended up underground.