mRender called multiple times

Hi
can someone explain to me why the function defined for the mRender property is
called multiple times per row?
As you can see here:
http://jsfiddle.net/6JCH2/13/

fnRowCallback and fnCreatedCell are called the exact number of times (3) while
the function defined by mRender is called multiple times per row

I was using fnRender for this and it was functioning as expected, am I doing something wrong?

Thanks