I discovered a race condition in sendrawtransaction. For details: see my comment in https://github.com/bitcoin/bitcoin/commit/1d46fe3327f6645fd79b442cd72ef422418c1a50.

If you send a raw transaction which has already been broadcasted, then you don't know whether you'll receive an RPC_TRANSACTION_ALREADY_IN_CHAIN exception, since you don't know whether a new block has just been received, which includes the transaction. There are use cases where such RPC_TRANSACTION_ALREADY_IN_CHAIN occurrences do not indicate an error; however, since this type of occurrence is very rare, developers are not likely to be aware of the possibility, and silence the exception. As a result, applications can potentially experience hard-to-diagnose, very rare errors.

I think the core of the problem is that sendrawtransaction tries to combine two use cases:
A: publish a transaction on the Bitcoin network
B: re-transmit an already known transaction to peers
RPC_TRANSACTION_ALREADY_IN_CHAIN might make sense for B, but for A (which is, IMHO, the primary use case) it is confusing.

}},
                        {RPCResult::Type::ARR, "outputs", "",
                        {
                            {RPCResult::Type::OBJ, "", "",
                            {
                                {RPCResult::Type::OBJ, "redeem_script",  true, "",
                                {
                                    {RPCResult::Type::STR, "asm", "The asm"},
                                    {RPCResult::Type::STR_HEX, "hex", "The hex"},
                                    {RPCResult::Type::STR, "type", "The type, eg 'pubkeyhash'"},
                                }},
                                {RPCResult::Type::OBJ, "witness_script",  true, "",
                                {
                                    {RPCResult::Type::STR, "asm", "The asm"},
                                    {RPCResult::Type::STR_HEX, "hex", "The hex"},
                                    {RPCResult::Type::STR, "type", "The type, eg 'pubkeyhash'"},
                                }},
                                {RPCResult::Type::ARR, "bip32_derivs",  true, "",
                                {
                                    {RPCResult::Type::OBJ, "", "",
                                    {
                                        {RPCResult::Type::STR, "pubkey", "The public key this path corresponds to"},
                                        {RPCResult::Type::STR, "master_fingerprint", "The fingerprint of the master key"},
                                        {RPCResult::Type::STR, "path", "The path"},
                                    }},
                                }},
                                {RPCResult::Type::OBJ_DYN, "unknown", "The unknown global fields",
                                {
                                    {RPCResult::Type::STR_HEX, "key", "(key-value pair) An unknown key-value pair"},
                                }},