The new Auto Ripple features in Vegas 4.0 are pretty cool! It automatically moves the events in all affected tracks when you move/trim one event.
You can choose between "Affected Tracks", "Affected Tracks, Bus Tracks, Markers & Regions" and "All Tracks, Markers & Regions". 
But I'm wondering about the rule. How are the "affected tracks" determined? It indeed seems to only move the events in certain tracks. What's the common denominator?