Hi. My xperia z2 has the same problem. It started weeks after using 4.4.4 update with no problems , then one day the MDR-NC31E started being detected as a stereo microphone. I have repaired it via pc companion, also i've reflashed 4.4.2 both without solving it.
I've also noticed that after plug in a normal pair of headphones, that by the way all of them work perfectly, and plug in again the noise cancelation ones, sometimes the phone recognises it correctly as NC but only delivering sound to the left earpice. when this happen, if i move the jack conector of the headphones making it do more pressure with the phone pins the right earpice start to work. I think that is not 4.4.4 related because in 4.4.2 it fails too even selecting the correct 5 pins accesory in options (it is detected automtically in 4.4.4 but there is a selection menu in the 4.4.2).
Some spanish forum say that its actualy a hardware problem with the jack conector of the phone.
Symptoms are: MDR NC31E detected as microphone, rarelly sometimes detected correctly but with no sound in right earpiece. Stardard headphones works without problems plugged in the phone, also MDR NC31E works perfectly in other devices (phones, pc, tv...) obviously without noise cancelation. Also working correctly in my friend Z3.
Hope this help a little. VERY BAD SONY!!
Mine is going to service under warranty because i havent been able to get a solution. this is the second time sending it to the service, first was for a vibration issue (ramdomly stopped working) it took 3 times to get it correctly fixed...let's see this one.
