It may be that Akira came across a bad batch, or was simply unlucky to find several bad samples at the same time, or indeed the newer lenses are flawed compared to the earlier production. It is very difficult to know for certain either way.
Usually, an irregular shaped aperture becomes noticeable only at smaller apertures (bigger f-number). If you mainly shoot at wider-medium apertures, or are not too concerned about the shape of out-of-focus highlights, then it is not an issue. If the background has no bright point sources of light or reflections, you won't even notice the irregular shape in your pictures. If it is important to you, make sure you buy from somewhere with a good return policy, or buy from a shop where you can inspect the lens first.