[waterlesscloud]

I was looking into that, but got sidetracked and found this comment from the ref client's lead dev...

sendtoaddress didn't always return a transaction id. It was changed to do that to facilitate bookkeeping. Sort of ironic.

https://bitcointalk.org/index.php?topic=807.0

[patio11]

To be fair, he made that addition before anyone, including probably Satoshi Nakamoto, knew that the Bitcoin "protocol" allowed transaction IDs to change at will for up to ~1 hour after them being sent.