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 (!fFileBacked)
        return DB_LOAD_OK;
    fFirstRunRet = false;
    DBErrors nLoadWalletRet = CWalletDB(strWalletFile,"cr+").LoadWallet(this);
    if (nLoadWalletRet == DB_NEED_REWRITE)
    {
        if (CDB::Rewrite(strWalletFile, "\x04pool"))
        {
            LOCK(cs_wallet);
            setKeyPool.clear();
            
            
            
        }
    }
    if (nLoadWalletRet != DB_LOAD_OK)
        return nLoadWalletRet;
    fFirstRunRet = !vchDefaultKey.IsValid();
    uiInterface.LoadWallet(this);
    return DB_LOAD_OK;
}
DBErrors CWallet::ZapSelectTx(vector<uint256>& vHashIn, vector<uint256>& vHashOut)