As I recall, we had a thread like this several years ago in answer to a question I had about C25 used in low temperature conditions. It is my impression that we concluded that separation could occur depending on the dewpoints or vapor pressure of the gases, but I can't find the thread to verify this. This had to do with the CO2 condensing out and the argon being used, thus spoiling the mixture.
Would rolling a cylinder under high pressure actually remix gases? (I can see some physics operating with a Co2 cylinder where a liquid gas is involved, but wouldn't separated gases behave like a liquid and simply return to their respective positions when the cylinder is upright again?).