I understand that refunds won't get back to the sender when sent from an online wallet, but when sent from the client isn't there a "from" address?
No, there isn't. Coins are never sent from an address, only to an address. Some of the coins in a transaction may have been claimed by particular addresses, but that is not a requirement, nor need a transaction have only one address used to claim the coins used in it. For example, I could mine a block and send your address the 50 coins I get for mining it. What's the "from" address in that case?