Multisig doesn't work unless all keys were generated from the current wallet?
The built-in multisig support in the reference client is only a proof-of-concept. As until recently (and still) the wallet did not deal well with coins being spent outside of its control, it was decided to only allow spending multisig coins when you have all keys. Of course that completely defeats the purpose of multisig, but proper support for it requires separate tools anyway (to pass the partially signed transactions around, etc).

However, the planned watch-only wallet support does allow watching multisig addresses too (in fact, any script at all), which will appear in listunspent. Clearly, the regular sendtoaddress &amp; co RPCs cannot spend these coins, but it does give the ability to track them.