If they are small enough to show full size they won't expand. If they're bigger than will fit in the page, they will expand. Bill's G+ photos I assume he drag-dropped in here. So he just got the thumbnails which are fairly small, square, and won't expand on clicking.
Bill, that's a bug then. I'll look at the admin side and see what can be done. Can you email me the picture in question?
On a side note, how did you add your profile pic? It's been broken for me.