I bought my XC10 back in January (2016) and have been very happy with the quality of the images/footage. This 'Ghosting' or temporal noise reduction (possibly) has also shown up on my footage (see bellow) - and I've been following this thread on the issue. Having had a close look at the artefact I can pretty much say with certainty its an error in the calculation of how Canon integrate values from one frame to the next when calculating for motion blur. Basically the maths is off and creating a 'rounding error' so the pixel bins either hold an 'over shoot' or 'under shoot' value - so you get this characteristic 'zoning' of luminance values. Its a bit like the posterising effect (thresholding) one can achieve when reducing the bit depth of an image. So what is causing this ... hopefully it's a firmware only issue, in which case the frame to frame integration algorithm needs re-writing, or it is something done in hardware ... which means a fault in the DIGIC DV 5 chip. Canon will need to check in the later case if it is a batch issue or systemic. Let's hope it only requires a firmware update! The 'good' thing is that if it is (as I surmise), then the solution is just a question of maths - but the problem is how that is implemented - at chip level in hardware or a firmware 'bug'.
(I should add, this could also will explain why this is less evident on HD footage as it has 4x more 'integration' as a reduction from 4K in spatial resolution - equivalent of averaging down to a quarter sized image.)
One test we could try is running at a higher frame rate (HD only) and seeing if the artefacts are reduced or increased further for the same amount if spatial moment - in other words more samples over a given time frame and spatial transfer.