Just to update this thread, neither 0x08 or 0x18 change the playback order.
3.6.12. Set random playbackRandom playback of the whole storage device 7E FF 06 18 00 00 00 FE E3 EF1).This command is used to randomly play sound files in the storage device according to physical sequence and nomatter if there is a folder or not in the device. The first sound file that is conducted to be played is the first one in thedevice.
I think the function attached to the play next button just calls the next track, not a random track.
Of course - did you expect "play next" to play a random song?