I've had a similar issue. Bizarrely my service indicator for a rear brake change decreased to 3000 miles & then started increasing again! Its now down again to 1200 miles. I have no idea what's going on.
Also had some strange behaviour with the indicator for the oil level. Sometimes it tells me that the oil level is too high & shoudl be checked and at other times tells me that the oil level is OK. I've not put any oil in since it was last serviced by my local dealer.
My feeling is that the CBS system is not very reliable!