Maybe they have some purpose, but it isn't immediately obvious. I tried Tree & List mode, they're never populated.

![image](https://user-images.githubusercontent.com/13134193/33488849-04a2c8a6-d6ed-11e7-85c3-5c05f1ec5346.png)

* Bitcoin-Qt 0.15.1 for Ubuntu 16.04 x64 (from http://ppa.launchpad.net/bitcoin/bitcoin/ubuntu xenial/main amd64)

Note: I just noticed I'm *not* seeing this on Ubuntu 17.10 x64 with 0.15.1 downloaded from bitcoincore.org. 

![image](https://user-images.githubusercontent.com/13134193/33491553-9584dc62-d6f5-11e7-9ba7-e074e0e36151.png)


if (fWitness)
        {
            
            
            
            nBytes += 2; 
            nBytes += nQuantity; 
        }
        
        if (CoinControlDialog::fSubtractFeeFromAmount)
            if (nAmount - nPayAmount == 0)
                nBytes -= 34;
        
        nPayFee = model->wallet().getMinimumFee(nBytes, *coinControl(), nullptr , nullptr );
        if (nPayAmount > 0)
        {
            nChange = nAmount - nPayAmount;
            if (!CoinControlDialog::fSubtractFeeFromAmount)
                nChange -= nPayFee;
            
            if (nChange > 0 && nChange < MIN_CHANGE)
            {
                CTxOut txout(nChange, static_cast<CScript>(std::vector<unsigned char>(24, 0)));
                if (IsDust(txout, model->node().getDustRelayFee()))
                {
                    nPayFee += nChange;
                    nChange = 0;
                    if (CoinControlDialog::fSubtractFeeFromAmount)
                        nBytes -= 34; 
                }