Oh, I was expecting this to act more like the working set, but it seems like the working set is a bit funny too. In that example, seeing "styles.css - sandbox" even though sandbox is the root folder gives me the impression that sandbox is somewhere below the root.

In the working set, these files are displayed as:

styles.css - sandbox
styles.css - sandbox/folder
styles.css - parent/folder

So it looks like the working set labels include the project folder name as well.