That's because you're applying the curve internally in Capture One (which is always in 16-bit mode), and then downsampling to 8-bit after the curve is applied. Your test is not valid. Export the dark image into Photoshop, convert to 8-bit mode, then apply the curve, and you'll get something much different.
i said, for twice, the curve was applied in photoshop.
the question is:
there is huge difference between 16b and 8b images' histogramafter a very steep curve, the 8b image's histogram did turn very discrete whereas the 16b image's histogram remained continuous.
BUT why there is no such obvious difference when comparing the images, on an Apple Cinema Display HD.
there is nearly no difference in shadow
a little bit more in mid-tone, and finally gets a little bit obvious in hightlight
maybe PhaseOne's lossless compression is in fact not lossless
maybe 16 bit images only depict CCD noise more smoothly than 8 bit ones for this generation of MFDB. (that's why the histogram is smoother but the image is not)