usb music

[Auris Geezer]

I've loaded my itunes library (4000 tracks, some of which are full albums) onto a usb drive and it plays great.  However, the player/system keeps reverting to random play.  I've unchecked the random button in settings, but it seems to revert to "random" after every time I park up.  Any clues?  Probably related, but if I press the "up" button on the steering wheel control, if I'm playing for example track 1, it doesn't go to track 2, but some other random track.  Lkewise, if I press the down button, I'd expect it to go back to the last track, but no, another random track. 

It's not a massive issue, but if I can fix it, that would be great.