As I think about this, having those vacuum lines piped together could cause the vacuum between the 3 throttle bodies to potentially balance, even when they aren't , giving an inaccurate throttle body adjustment (the throttle bodies could be badly out of adjustment but indicate they are balanced). Hooked up like that could act like a vacuum leak allowing vacuum to transfer from one throttle body to the other. Just a calculated guess having never checked how those vacuum lines for the Cali versions interact.