Your wallet has a default address used for sending
Absolutely notNo still wrong. It doesn't. Every tx is simply sending a prior tx output. There isn't a static address that all tx come from. If you have 5,000 different addressses with unspent outputs then your future tx (in aggregate) will be coming from those 5,000 outputs.
Period. Default, static, pre-set = all wrong. All tx inputs are prior tx output. Period. They will be from any address you received funds at.
Do you think you could possibly explain this in plain English
?Ive done some research and I think I get it.
Any address attached to your wallet that has received coins can be selected (automatically by the bitcoin client) as a "From" address for the same wallet.
So any funds sent from a real wallet can be refunded (or bets paid) by sending N btc back to the "From" address.
Most online wallets MTGOX, walletbit etc do not assign a wallet per account, your funds are held in a DB.
The deposit addresses provided are for their own wallet, their software monitors the incoming transactions to each address and if its matched to a pending deposit the funds are assigned to the account.
When Sending funds from an online wallet again the funds are deducted from your account then sent from their wallet, any transfers sent back to the From address used are checked for a pending deposit, none are found so the site takes it as a "donation".
edited: grammar, punctuation, flow and spelling. (noticed how bad my sentence was when Stephen quoted it )
