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.

{
    {
        LOCK(cs_wallet);
        CWalletDB walletdb(strWalletFile);
        BOOST_FOREACH(int64_t nIndex, setKeyPool)
            walletdb.ErasePool(nIndex);
        setKeyPool.clear();
        if (IsLocked())
            return false;
        int64_t nKeys = max(GetArg("-keypool", DEFAULT_KEYPOOL_SIZE), (int64_t)0);
        for (int i = 0; i < nKeys; i++)
        {
            int64_t nIndex = i+1;
            walletdb.WritePool(nIndex, CKeyPool(GenerateNewKey()));
            setKeyPool.insert(nIndex);
        }
        LogPrintf("CWallet::NewKeyPool wrote %d new keys\n", nKeys);
    }
    return true;
}
bool CWallet::TopUpKeyPool(unsigned int kpSize)