This happened to me after upgrading from Mountain Lion. It's a pain, but can be fixed quite easily.
Open up Terminal.app, and enter:
sudo rm -rf ~/.Trash
Bear in mind, this will also remove any items currently in the Trash.
Now, create an empty folder or file on your Desktop, and drag it to your Trash icon. This will recreate the .Trash folder automatically.
If you're lucky, it will revert to expected behaviour and now display correctly when items are contained within!