Built against `master` branch 801dd40666d1e6009920ad3ff755c7bb993b2a62:

If I have no wallet.dat file and run:

    bitcoind -usehd=0

A new wallet.dat file is created and an HD seed is assigned.

I see an error message in the source:

    "Error loading %s: You can't disable HD on an already existing HD wallet or create new non-HD wallets."

but that doesn't get shown because `fFirstRun` is true, and so the code which checks for `-usehd` values doesn't run.

If it's no longer possible to create non-HD wallets, specifying -usehd=0 when creating a wallet should be an error, and not get silently ignored.
if (std::string::npos != nSepPos)
            {
                CDataStream ss(std::vector<char>(strComment.begin() + nSepPos + 1, strComment.end()), s.GetType(), s.GetVersion());
                ss >> mapValue;
                _ssExtra = std::vector<char>(ss.begin(), ss.end());
            }
            ReadOrderPos(nOrderPos, mapValue);
        }
        if (std::string::npos != nSepPos)
            strComment.erase(nSepPos);
        mapValue.erase("n");
    }
private:
    std::vector<char> _ssExtra;
};
/** 
 * A CWallet is an extension of a keystore, which also maintains a set of transactions and balances,
 * and provides the ability to create new transactions.
 */
class CWallet final : public CCryptoKeyStore, public CValidationInterface
{
private:
    static std::atomic<bool> fFlushScheduled;
    std::atomic<bool> fAbortRescan;
    std::atomic<bool> fScanningWallet;
    /**
     * Select a set of coins such that nValueRet >= nTargetValue and at least
     * all coins from coinControl are selected; Never select unconfirmed coins
     * if they are not ours
     */