Hearing many talk of this issue on this very very good lens that also made me too much worry on it, along this first week of this lens, the picture testing are to checked whether this phenomena is made the lens flaw.
From this sequences, it told, yes it shift @ f4.0 onward and most effected is on f4.0 and f5.6 after f8.0 then the dept of field is more than enough to cover the sharpness.
And even at f4.0 and 5.6 the focus point still sharp enough, sure it not 100% punctual the most sharpest point but it more than enough for the real world photos.
Have a look by your self.