I did some more testing this morning and found that when any of the zones on the main board are activated ALL zones turn on. But if I only turn the zone on the expansion board on then the zones on the main board do not come on.

Zone 1 – Master
Zones 2-8 – Valves
Expansion Zone 1 (zone 9) – Valve

So if I turn on any zone 2-8 the master AND all zones 2-8 open up. But if I turn on zone 9 only the master and zone 9 open up.