I'm gonna go out on a limb and suggest that this is because its not actually been committed to the blockchain or its not a complete transaction. We're gonna dig in this eve and find out if a partially signed tx has the same tx_id as the broadcast tx. I'd feel like off that back of your investigation @peg its probably different.

There's no reason why we can't send partially signed tx's over scuttlebutt (with other information for transparency / accountability), and then broadcast once the correct number of signatories have been collected. Dan and I have been riffing on this idea this week and while we setup a multisig using the bitcoin-cli last eve.