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.

pindex = chainActive.Next(pindex);
            if (GetTime() >= nNow + 60) {
                nNow = GetTime();
                LogPrintf("Still rescanning. At block %d. Progress=%f\n", pindex->nHeight, Checkpoints::GuessVerificationProgress(chainParams.Checkpoints(), pindex));
            }
        }
        ShowProgress(_("Rescanning..."), 100); 
    }
    return ret;
}
void CWallet::ReacceptWalletTransactions()
{
    
    if (!fBroadcastTransactions)
        return;
    LOCK2(cs_main, cs_wallet);
    std::map<int64_t, CWalletTx*> mapSorted;
    
    BOOST_FOREACH(PAIRTYPE(const uint256, CWalletTx)& item, mapWallet)
    {
        const uint256& wtxid = item.first;
        CWalletTx& wtx = item.second;
        assert(wtx.GetHash() == wtxid);
        int nDepth = wtx.GetDepthInMainChain();
        if (!wtx.IsCoinBase() && (nDepth == 0 && !wtx.isAbandoned())) {
            mapSorted.insert(std::make_pair(wtx.nOrderPos, &wtx));
        }
    }
    
    BOOST_FOREACH(PAIRTYPE(const int64_t, CWalletTx*)& item, mapSorted)