Cannot right click on unstaged file to add to index

Expected: I should be able to right click on an unstaged file (or multiple selected unstaged files) and add it to the index from the File Status tab.
Observed: "Add to Index" is not in the list of options. "Unstage from index" is grayed out.

I can stage files by checking the checkbox next to each file name. The right-click to stage is especially useful when selecting multiple, but not all unstaged files.

Screenshot: http://screencast.com/t/9PI4tVDq6UA