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.

+ HelpExampleCli("createrawtransaction", "\"[{\\\"txid\\\":\\\"myid\\\",\\\"vout\\\":0}]\" \"[{\\\"data\\\":\\\"00010203\\\"}]\"") +
                            "\nConvert the transaction to a PSBT\n"
                            + HelpExampleCli("converttopsbt", "\"rawtransaction\"")
                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    RPCTypeCheck(request.params, {UniValue::VSTR, UniValue::VBOOL, UniValue::VBOOL}, true);
    
    CMutableTransaction tx;
    bool permitsigdata = request.params[1].isNull() ? false : request.params[1].get_bool();
    bool witness_specified = !request.params[2].isNull();
    bool iswitness = witness_specified ? request.params[2].get_bool() : false;
    const bool try_witness = witness_specified ? iswitness : true;
    const bool try_no_witness = witness_specified ? !iswitness : true;
    if (!DecodeHexTx(tx, request.params[0].get_str(), try_no_witness, try_witness)) {
        throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "TX decode failed");
    }
    
    for (CTxIn& input : tx.vin) {
        if ((!input.scriptSig.empty() || !input.scriptWitness.IsNull()) && !permitsigdata) {
            throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "Inputs must not have scriptSigs and scriptWitnesses");
        }
        input.scriptSig.clear();
        input.scriptWitness.SetNull();
    }
    
    PartiallySignedTransaction psbtx;
    psbtx.tx = tx;
    for (unsigned int i = 0; i < tx.vin.size(); ++i) {
        psbtx.inputs.push_back(PSBTInput());