I think I shared my experiences about this on another thread. Over about 60-70 flights in J on QR over the last 18 months, I've had no issues at all on 95% of the flights, and been challenged about (and had to check in) my cabin baggage on the other 5%. Typically, my main cabin bag weighs 11-13kg, and my second shoulder bag weighs about 5kg. No clear explanation for the patterns I've observed, which have not tracked airports in any discernible way. It just seems to depend entirely on the check-in agent you get, and their attitude towards applying the rules to the letter.