Relax. You're not doing anything wrong. Why not give your ID if asked?
Anyone behind the desk at the MC can handle your transaction if they've passed the required training. What difference does it make what their status is? I've had my money order transactions handled by temporary cashiers filling in on a break and store managers. As long as they can push the keys to complete the transaction, why does it matter?
Just asking. People here seem to be discussing the ID situation a lot, so I, being new to this, was wondering if being asked for ID was horrible and I should be running for the hills or something.