Depth of field & Transparency - Focus behaviour

Hi Guys,
take a look at the sphere in the bottom left.
In the 2 images i’ve just changed the material.
Why when using a transparent material the part of the sphere in the second image has blurred edges on the top? (it is out of focus as the stuff on the back)

Thanks a lot!

enable: output velocity in the material specs
and uncheck Render After DOF