When a pass of CreateTransaction fails to select enough bitcoin to meet the nFeeNeeded the next pass through may select a far smaller collection of inputs.  Currently it will continue to use the old fee amount based on the larger set of inputs, which can cause a non-trivial over-payment.

This may be the cause of the behavior reported here: https://www.reddit.com/r/Bitcoin/comments/5ltw5n/bitcoin_core_v0131_sends_enormously_high_fee/

Long ago fixing this was tricky due to a catch-22 between signing the transaction and knowing how much fee was required.  But after #9465 the whole algorithm will run using a dummy signature, so when there is already a change output fixing up the fee after finding a sufficient transaction should be a matter of a ~2 line change.

CWalletDB walletdb(strWalletFile);
    return walletdb.ListAccountCreditDebit(strAccount, entries);
}
bool CWallet::AddAccountingEntry(const CAccountingEntry& acentry)
{
    CWalletDB walletdb(strWalletFile);
    return AddAccountingEntry(acentry, &walletdb);
}
bool CWallet::AddAccountingEntry(const CAccountingEntry& acentry, CWalletDB *pwalletdb)
{
    if (!pwalletdb->WriteAccountingEntry_Backend(acentry))
        return false;
    laccentries.push_back(acentry);
    CAccountingEntry & entry = laccentries.back();
    wtxOrdered.insert(make_pair(entry.nOrderPos, TxPair((CWalletTx*)0, &entry)));
    return true;
}
CAmount CWallet::GetRequiredFee(unsigned int nTxBytes)