As the Chevrolet Corvette enters the last year of the C6 generation, it’s surprising to see that the popular sports car – which has earned kudos for its quality for years ? has suddenly landed on the listing for Least Reliable listing in the latest Consumer Reports Annual Auto Survey.

Our research on the Web couldn’t turn up the reason for this sudden poor rating, but at least the Corvette can take solace in the fact that muscle cars in general appear to have had a rough year.

In the latest reliability rating, 11 out of 21 sporty cars had average-or-better reliability. Last year, 13 out of 16 achieved that rating.

A year ago, only three models were below average for predicted reliability. This year, there are 10 such models.

?Each year, car reliability trends begin surfacing as we look at data by brand and car type, with periodic spikes common around redesigns and new technology. As is often the case, the muscle and otherwise sporty cars are seeing much reliability activity in the latest Consumer Reports Annual Auto Survey,? a press release from Consumer Reports says.

The Chevy Camaro continues to have reliability woes, according to Consumer Reports, including problems with body hardware, which includes windows, locks and latches, doors or sliding doors, trunk, mirrors, seat controls, seat belts, sunroof, and convertible top. Also suffering reliability problems are the Ford Mustang and Dodge Challenger.

Interestingly, the Challenger fared well in the ranking last year but in the 2012 survey was plagued with problems in squeaks and rattles, body hardware, brakes, and audio system.

But there is hope for the low-ranked. The top sports car this year is the Nissan 370Z. Last year, it was at the bottom of the ratings.

?Key reasons for its volatility is the small survey sample size and the fact that Nissan may be actually sorting out bugs,? Consumer Reports says. ?Periodically, we do not receive survey responses on more than 100 Z-cars detailing issues?our minimum threshold. This means that even though the car has been around for years, its prediction is occasionally not based on a three-year data set, and this is noted in our ratings.?

Ironically, in February, the same Consumer Reports unveiled its 2012 rankings for the best and worst vehicles from Detroit’s Big Three and rated the Corvette Z06 the highest among vehicles from the United States.

?The Corvette offers impressive performance, with a relatively comfortable ride and very capable handling,? Consumer Reports said back then. ?The automatic transmission has paddle shifters, and the manual versions have a launch-control feature for smooth takeoffs.?

Overall, just nine months ago, the Z06 was judged as the world’s eighth best car, tying with the Hyundai Genesis 3.8 sedan and Toyota Camry XLE V6 with a score of 92/100.

Confusing? Yes.