It seems mp3 codec in SFP16 changed. Since Sony SF through SFP15, SFP had been using the "Xing" codec. In SFP16 it seems that it changed to FhG (Fraunhofer) or Lame. I checked the details of MP3 Custom Settings -> Stereo Encoding and Property Marking options are no longer available. Maybe this is the reason some users have reported problems saving in MP3 format.