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.

std::vector<COutput> vAvailableCoins;
            AvailableCoins(vAvailableCoins, true, coinControl);
            nFeeRet = 0;
            
            while (true)
            {
                nChangePosInOut = nChangePosRequest;
                txNew.vin.clear();
                txNew.vout.clear();
                wtxNew.fFromMe = true;
                bool fFirst = true;
                CAmount nValueToSelect = nValue;
                if (nSubtractFeeFromAmount == 0)
                    nValueToSelect += nFeeRet;
                double dPriority = 0;
                
                for (const auto& recipient : vecSend)
                {
                    CTxOut txout(recipient.nAmount, recipient.scriptPubKey);
                    if (recipient.fSubtractFeeFromAmount)
                    {
                        txout.nValue -= nFeeRet / nSubtractFeeFromAmount; 
                        if (fFirst) 
                        {
                            fFirst = false;
                            txout.nValue -= nFeeRet % nSubtractFeeFromAmount;
                        }
                    }
                    if (txout.IsDust(::minRelayTxFee))
                    {