Ok let see if i can explain what i found
If you boot build 548 then immediately try to change tracks it will perform something similar to IGR. If you change albums directly after bootin this build it will act normally.
Cant select .wma when using the Audio Player to open file but when u select a .wma from the File Explorer it will begin to play the song no problem.
When first booting Build 548 you can swithc sons like normal using the white button and dpad combo (quick song select). Because of the new audio player of course the GUI is brought up while using "quick song select" now.
You can hit the "b" button to exit the Audio Player and navigate thru menus like normal while listening to the song you picked. When the Audio player is up and you press "start" to "Open File" and select a .wav or .mp3 to play it will play as usual. If after that you try to selct another son and hit "b" to exit the GUI another song will be played at random.
If that was confusing let me know so I can try to explain it better
EDIT: Here are my Audio Settings in the Control Panel
Play Music: Both
Random Music: Yes
Surround 5.1: Yes