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.
return true;
}
void CWallet::MarkDirty()
{
    {
        LOCK(cs_wallet);
        for (std::pair<const uint256, CWalletTx>& item : mapWallet)
            item.second.MarkDirty();
    }
}
bool CWallet::MarkReplaced(const uint256& originalHash, const uint256& newHash)
{
    LOCK(cs_wallet);
    auto mi = mapWallet.find(originalHash);
    
    assert(mi != mapWallet.end());
    CWalletTx& wtx = (*mi).second;
    
    assert(wtx.mapValue.count("replaced_by_txid") == 0);
    wtx.mapValue["replaced_by_txid"] = newHash.ToString();
    CWalletDB walletdb(*dbw, "r+");
    bool success = true;
    if (!walletdb.WriteTx(wtx)) {
        LogPrintf("%s: Updating walletdb tx %s failed", __func__, wtx.GetHash().ToString());
        success = false;
    }
    NotifyTransactionChanged(this, originalHash, CT_UPDATED);
    return success;
}
bool CWallet::AddToWallet(const CWalletTx& wtxIn, bool fFlushOnClose)