I went back and looked at the uncropped IS test shots from my M11-22 review, and the edges (well, the one edge with subject matter other than a blank wall) doesn't seem noticeably soft. However, that was my first review and only with subsequent lenses did it occur to me to have a tripod shot for comparison, so I can't say definitively that there's no loss of edge sharpness with IS on the M11-22.
Would you be willing to share your test images?
Also, are you giving the IS time to 'settle in'? It takes about 0.5 s for the IS system to effectively stabilize. In prior testing with the 100/2.8L Macro and 600/4L II, I found that if you just press the shutter from finger off to image capture at one go, the result can be worse than handholding without IS.