When you create a post and select Image Post Format type, the URL that you enter in the
Image click-through link field, is not being used when you view the actual post. Instead, the image is actually linking to the image file.
I was originally experiencing this issuse on an existing 3.6 install that I had. To confirm the problem, I created an entirely new fresh site, imported the Theme Test unit data and then updated to the latest build, 3.6-beta3-24280. I'm also running Twenty Thirteen.