Aah yes that's what the problem was with us now you mention BG, when we registered Zander's birth we didn't have the medicare card updated yet so they didn't have his medicare details.
i think a lot of people had this issue Sarah so the claim is all done together now - the only way it's not linked up is if you say you're not happy for centrelink/fao to collect your medicare number and link the details... most people do the automatic option - soooooooo much easier!