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.

fChangeCached = false;
        nDebitCached = 0;
        nCreditCached = 0;
        nImmatureCreditCached = 0;
        nAvailableCreditCached = 0;
        nWatchDebitCached = 0;
        nWatchCreditCached = 0;
        nAvailableWatchCreditCached = 0;
        nImmatureWatchCreditCached = 0;
        nChangeCached = 0;
        nOrderPos = -1;
    }
    ADD_SERIALIZE_METHODS;
    template <typename Stream, typename Operation>
    inline void SerializationOp(Stream& s, Operation ser_action) {
        if (ser_action.ForRead())
            Init(NULL);
        char fSpent = false;
        if (!ser_action.ForRead())
        {
            mapValue["fromaccount"] = strFromAccount;
            WriteOrderPos(nOrderPos, mapValue);
            if (nTimeSmart)
                mapValue["timesmart"] = strprintf("%u", nTimeSmart);
        }
        READWRITE(*(CMerkleTx*)this);
        std::vector<CMerkleTx> vUnused; 
        READWRITE(vUnused);
        READWRITE(mapValue);
        READWRITE(vOrderForm);