Mine did this a couple of years ago on my Espace III 2.2Dci for about 6 months where the mileage shot from 52,000M to 87,000M and then remained static. 6 months later it started working again with the mileage returning back to normal and the original 52000M. It never added any mileage for those 6 months and has been fine for the last 2 years.
Luckily this happened between MOT's and was never recorded as I still haven't reached the 87,000M post yet.