Lumia 920 here, just noticed this week when using the above mentioned ear buds, they work fine for the first call, however for the second call only the left ear works and no sound comes out of the right ear bud. Only way to fix it is to turn the phone off and then back on. It then works for the first call, but never again after that. Ear buds worked flawlessly prior to the 8.1 Preview update.