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.

else
            pindexRescan = chainActive.Genesis();
    }
    if (chainActive.Tip() && chainActive.Tip() != pindexRescan)
    {
        
        
        
        if (fPruneMode)
        {
            CBlockIndex *block = chainActive.Tip();
            while (block && block->pprev && (block->pprev->nStatus & BLOCK_HAVE_DATA) && block->pprev->nTx > 0 && pindexRescan != block)
                block = block->pprev;
            if (pindexRescan != block) {
                InitError(_("Prune: last wallet synchronisation goes beyond pruned data. You need to -reindex (download the whole blockchain again in case of pruned node)"));
                return NULL;
            }
        }
        uiInterface.InitMessage(_("Rescanning..."));
        LogPrintf("Rescanning last %i blocks (from block %i)...\n", chainActive.Height() - pindexRescan->nHeight, pindexRescan->nHeight);
        nStart = GetTimeMillis();
        walletInstance->ScanForWalletTransactions(pindexRescan, true);
        LogPrintf(" rescan      %15dms\n", GetTimeMillis() - nStart);
        walletInstance->SetBestChain(chainActive.GetLocator());
        nWalletDBUpdated++;
        
        if (GetBoolArg("-zapwallettxes", false) && GetArg("-zapwallettxes", "1") != "2")
        {
            CWalletDB walletdb(walletFile);
            BOOST_FOREACH(const CWalletTx& wtxOld, vWtx)