Kent,
>have your lens been this way all time, or have there been any incident causing this?<
It's always been this way, but it was not new when I bought it, and is out of warranty. The lens itself (MM model) is in very good condition otherwise, optically perfect, no barrel markings or wear of any kind. I noticed it more or less by accident because the exposure readings I was getting showed around 2/3 stop slower than my Planar 50, so I got all the lenses out and all the bodies out, and compared meter readings (fairly unscientifically). The Distagon 28 always showed slower. So I looked closely at the aperture blades, and at f2.8 they seemed to still be there are the edge of the lens, where the other lenses I have showed only glass.
I did contact Kyocera UK and they told me to send it to Contax in Germany, but I haven't done that, since what I hear from this list is that I'd be cheaper buying another. Exposures themselves seem to be fine, so I can live with that, and I don't think I have the courage to open a lens. It's just mildly annoying that a CZ lens should be 'out of tolerance' like this.
Alex