Question for anyone that might know of the US Airways Altitude Awareness Program that was developed in the 1980s with ALPA to mitigate altitude busts.

In it, US Airways originally recommended the PM set the altitude preselector when the AP was engaged. Today, I understand this has been changed to the PF controlling the MCP selections etc with the AP engaged.

From a human factors standpoint, I am curious as to when or why there was a change from the PM to the PF selecting the altitude preselect. Does anyone have any background on why this change; what was/is AA's protocol?