I have played about 85 ranked games but I seem to have a problem with the ranked play ratings.

It seems to work OK for 5 to 7 games increasing when I win, decreasing when I lose. However, occasionally when I win it tells me my rating has been increased by the right amount but my new rating number has dropped. Last game I won, the computer told me my rating increased by 8 but the new rating was about 200 lower than before the game.

Is this normal, if not how I can fix the problem?

No, this isn't normal... there are some issues with ratings.

A request for a fix has been made in CM 11 Bug Fixes / Enhancements; but there has been no information on when an update will be released.