Sony is rolling a minor update to the Sony WALKMAN app for Xperia devices. New build version 8.0.A.0.4 follows a big update in the form of 8.0.A.0.3, which launched last week. As you can tell from the numbering, this latest update is likely to include bug fixes only. It should be rolling to Xperia Z series devices right now.
Thanks Jiakushi, Jag, Mohit and Uli!