Sure. You essentially can't rely on a particular wallet sending from an address they know about, or even from an address they can control.
The classic example is of a service using a shared wallet like Coinbase does. Coinbase maintains control of the keys of every piece of Bitcoin their clients own, and they have an external database that contains a record of how much Bitcoin they are holding on behalf of their clients. This allows them to keep the vast majority of the funds offline where they are invulnerable to attack. This system means that the "from" address is likely never correlated to the sender, and they have no control of where they send "from". Relying on a client to provide this information usually ends in disaster, as does sending refunds to an address you were sent "from".
Even for the reference client Bitcoin-QT addresses are disposable and almost never linked. Change from one transaction is sent to an entirely new address which done invisibly from the users perspective. There's more information about that on the wiki, change addresses in themselves are quite confusing.
The classic example is of a service using a shared wallet like Coinbase does. Coinbase maintains control of the keys of every piece of Bitcoin their clients own, and they have an external database that contains a record of how much Bitcoin they are holding on behalf of their clients. This allows them to keep the vast majority of the funds offline where they are invulnerable to attack. This system means that the "from" address is likely never correlated to the sender, and they have no control of where they send "from". Relying on a client to provide this information usually ends in disaster, as does sending refunds to an address you were sent "from".
Even for the reference client Bitcoin-QT addresses are disposable and almost never linked. Change from one transaction is sent to an entirely new address which done invisibly from the users perspective. There's more information about that on the wiki, change addresses in themselves are quite confusing.
https://en.bitcoin.it/wiki/Change