France 1868 - Napoleon With Misprint?

Recently I acquired a lot containing the 1868 Napoleon 20c (Scott 33, Yvert 29B, Michel 28A). On first glance I thought, "nice, unused, too bad of the graze on the left side". Close study revealed that the graze is not a graze but something went wrong during printing of the stamp (red arrows). Also, it's not unused but has a very light cancel (green arrow). A nice specimen, nevertheless!

This picture shows the stamp on the right, on the left another copy for comparison;



Scan in hi-res: http://imageshack.us/photo/my-image...3125916.jpg/

Now, I don't have experience with these kind of (incidental?) misprints. What would this mean for the value of the stamp?

These types of printing anomaly are most often caused by foreign matter (mostly paper scraps) getting into the press.

They can keep the ink from reaching the paper or ink parts of the stamp that would not ordinarily be inked.

It is interesting but not one of the listed varieties.

This is now a confirmed and known misprint 'CASE 94 PANNEAU A2', another sample (on letter): http://www.delcampe.net/page/item/i...guage,E.html