Just thought that some folk might find this one a bit amusing. I did it just completely out of random, but this -specific- spot next to the inventory box allows you to put another item in it. It won't auto-fill; you need to do this manually. Seems to work with any new saves, but didn't get to test with old ones. Here's a pic to show it off in action.
Yep, known bug; it's actually the first slot of the next row, so it (unfortunately? ) doesn't give you any more inventory slots.
