I am still a little confused about 'addresses'. If I have a wallet with BTC2.00 spread across 4 different addresses (0.50 in each) and I send BTC0.75 to somebody else, are 2 of my addresses randomly emptied and then BTC0.25 sent to a new change address?
Can addresses be split up into separate wallets, or do they share the same private key(s)?
yes, but that's just how bitcoin-qt.exe works, it does not have to work like that / someone could write a different program that say ... sends change to a specified change address instead of making a new one