I know it's not motion from the tapping the button because it remains clear if I take a screenshot of the preview which is more shaky than just pressing the screen.
I took a picture and a screenshot of the picture to show what I am talking about:
Preview / Captured image (click images for larger variants)
In the preview you can clearly see the texture of my shirt and the freckles on my face while on the captured image it is just a solid blur.
I asked this question on the Android Stack Exchange too but no one seems to know there so I thought I'd try here.
I am running completely Stock 4.3