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 (pwallet == 0)
        return 0;
    
    if (IsCoinBase() && GetBlocksToMaturity() > 0)
        return 0;
    if (fUseCache && fAvailableWatchCreditCached)
        return nAvailableWatchCreditCached;
    CAmount nCredit = 0;
    for (unsigned int i = 0; i < tx->vout.size(); i++)
    {
        if (!pwallet->IsSpent(GetHash(), i))
        {
            const CTxOut &txout = tx->vout[i];
            nCredit += pwallet->GetCredit(txout, ISMINE_WATCH_ONLY);
            if (!MoneyRange(nCredit))
                throw std::runtime_error("CWalletTx::GetAvailableCredit() : value out of range");
        }
    }
    nAvailableWatchCreditCached = nCredit;
    fAvailableWatchCreditCached = true;
    return nCredit;
}
CAmount CWalletTx::GetChange() const