I actually think it might be a combination of hardware and software issues. The hardware performance degrades over time (due to gunked-up grills or whatever), and the firmware updates made the hardware shortcomings more apparent.I do think its a hardware (microphone) thing. As the firmware hasn't changed since I got them.
Time to clean these things and see what happens.
Maybe those who aren't experiencing any issues are just fortunate to have squeaky-clean ears. (I'm not trying to be sarcastic -- it really might be that those who have less-waxy ears also have fewer or no issues with the ANC.)