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.

{
    if (GetBoolArg("-disablewallet", DEFAULT_DISABLE_WALLET)) {
        pwalletMain = NULL;
        LogPrintf("Wallet disabled!\n");
        return true;
    }
    std::string walletFile = GetArg("-wallet", DEFAULT_WALLET_DAT);
    CWallet * const pwallet = CreateWalletFromFile(walletFile);
    if (!pwallet) {
        return false;
    }
    pwalletMain = pwallet;
    return true;
}
std::atomic<bool> CWallet::fFlushThreadRunning(false);
void CWallet::postInitProcess(boost::thread_group& threadGroup)