Originally Posted by vapilot2004
Agreed but there is no normal operational reason for an oscillation of the resulting V path
Yes there is. As already stated in open descent it doesn't maintain a V/S, it maintains a speed.
As an example, with a sudden headwind increase (and subsequent IAS increase), the aircraft will raise the nose to adhere to the selected speed target, reducing the V/S in the process.
In a normal open descent, especially in varying wind conditions (as would be completely expected around mountainous terrain) then the V/S will change significantly. It's not unusual for variations between 1000fpm and 4000fpm.