Isn't it just a case of the restriction at MC768 of 230 knots being a maximum speed? But for whatever reason the FMGC has worked out that it needs to be at 220 its for its optimum profile in anticipation of the next restriction? I don't know the complex algorithm your FMS software is using, but maybe it's looked at the fact you are 5400 feet above profile and disregarded any benefit of trying to fly 230 to get down to it's level deceleration segment prior to the 220 restriction. Just a thought. Maybe the managed speed behaviour would be different if on profile?