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.
int nVersion = s.GetVersion();
        if (!(s.GetType() & SER_GETHASH))
            READWRITE(nVersion);
        READWRITE(vchPubKey);
    }
};
template <typename ContainerType>
bool CWallet::DummySignTx(CMutableTransaction &txNew, const ContainerType &coins) const
{
    
    int nIn = 0;
    for (const auto& coin : coins)
    {
        const CScript& scriptPubKey = coin.txout.scriptPubKey;
        SignatureData sigdata;
        if (!ProduceSignature(DummySignatureCreator(this), scriptPubKey, sigdata))
        {
            return false;
        } else {
            UpdateTransaction(txNew, nIn, sigdata);
        }
        nIn++;
    }
    return true;
}
#endif