checkboxes - Are round check boxes confusing or an accepted standard?

I was browsing dribbble.com today and came across a new post by one of the designers that I follow. He had posted a new modal form which was using rounded check boxes. I have never seen these before.

Are this an accepted standard, or are they confusing to the user (before they check them especially) because they look like radio buttons?

Update: Just found another place that uses them as well.

Update #2: After reading some of the comments, I realized this is present in iOS also, but I have never noticed. Also after going back Morgan's other work, I saw that his original design of this type of check box was a redesign of the current iOS one:

My guess as to where this came from is as a modification of the usual iOS delete button which is round. Since the only time the round check box shows up is when deleting messages, it must have been a clearer way to display that several messages were ready to be deleted, but they didn't give any thought to the fact that is looked like a radio button. It also seems to only be used when removing an item.

Answer

If I saw that in an interface - I would assume only one item can be checked, especially before any had been selected. Only the wording of the title would indicate to me that multiple selection is possible. I think this design would lead to a greater than normal number of people choosing a single item rather than a selection of items.

I don't see the benefit here in bucking accepted trends other than to make it all curvy everywhere, but pretty rounded rectangles would do the job just as well, be more intuitive and more standard.

I don't dislike the appearance from a pure graphical perspective - I just don't think it's right from the affordance perspective.

-- edit update --

I redesigned it with rounded squares:

-- further update --

As an interesting addendum - I found this (below) on a Google spreadsheets viewform survey (from UXPin) recently. It combines the outer shape of a checkbox, so that multiple-answer questions and single-answer questions have options that look quite similar in appearance, but the single-answer options have the inner circular shape of a radio button.

I had no confusion as to how it might be used, but I found this representation very unusual - in fact this was the first time I'd seen it. I find this quite interesting.