Hi Peter.
Apologies, it would appear that I had been causing the issue...
After playing around, I realised where I was going wrong.
Instead of pressing the play icon on a playlist title, I had been pressing the playlist name and then play on a specific item to start with.
This plays my selection but continues to randomize the entire library.
If you press the play icon on a playlist, it randomises and stays with the playlist.
All part of the learning curve I guess...
Many thanks
Carl