Spoke too soon......
I changed the WA_Globals file to read: $WAGLOBAL_Root_URL = "http://www.voyagermoon.com/";
The result is that someone purchasing a product on the .com domain has no problems. Paypal redirects them back to the confirm page as it should.
But - when someone purchases a product on the .com.au domain they end up back at .com with the message "the cart is empty".