One thing I've noticed is that when the system automatically rebooks into PZ it doesn't always use the most logical flights/connection. I've got no idea if it defaults into looking for flights with open PZ (or more available premium cabin inventory) first. Had an example earlier this year where it rebooked an EWR-SFO-OGG schedule change into something with a 9hr connection in SFO (albeit all in PZ) when much more logical connections existed (though without PZ inventory avaliable). In that case, then it's very much up to the agent you get to rebook again and get the PZ space opened on a better routing.

-FlyerBeek