Got a replacement lens today ... in god I trust (sort of) ...
Does 2 bad samples suggest a design issue rather than mis-alignment of optics ?
The behaviour is very odd. Symmetrically fine images at 12mm but the lower left corner issue at 60mm.
Usually centering issues are emphasized at long focal lengths but there isn't really anything to emphasize at 12mm.
I am really beginning to wonder whether this relates to the deactivated IS group on Oly cameras.