The A320 has a soft ALT mode in cruise, allowing for 50' altitude variations - is the -330 different in that respect?
Have looked and see no mention of this and never heard it spoken of during training. I am almost certain that the 330/340 does not have this soft alt mode. Also when flying I have never seen it deviating from the selected ALT (CRZ) without correcting to regain it, even by 10ft on the side the active AP is on.