I have a similar but different problem:
I've been able to sign and send single input transactions from a multisig address using bitcoind like this one:
https://blockchain.info/tx/68b45d27ca8405285b4d5490095bfad50ac94c314b75e82bd976e8b40d435408
But, after signing a spent from multiple inputs, I was unable to send the following transaction from bitcoind, it also failed on blockchain tx:
https://blockchain.info/tx/6bf129bc2ef572fbf61af3ff181dc080a69adf8d0951be55d3f6588534d3645d
I got it to work by transmitting it through the same service you did: coinb.in.
Why did the transaction not send from bitcoind? Do I need to connect to a certain node before I send?