I had the same issue some time ago - the short answer is that the JoinMarket protocol requires you to have the target address of a join in your wallet. I. e., patientsendpayment only works if you send to yourself, and then only if you import the target address into your JoinMarket wallet. I think there is some incentive to change the protocol to make it work as originally envisioned, but I don't think that actual work is already done on that.
Thanks, that's good to know.
I've also talked to belcher about this error from bitcoind's debug.log:
This occurs when a new transaction is detected, which was sent externally (e.g. not part of a joinmarket-transaction) to the joinmarket-wallet. This error can safely be ignored. If a yield-generator is running, he won't see the funds though until restarted.