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)


nPayAmount += amount;
        if (amount > 0)
        {
            CTxOut txout(amount, static_cast<CScript>(std::vector<unsigned char>(24, 0)));
            txDummy.vout.push_back(txout);
            fDust |= IsDust(txout, model->node().getDustRelayFee());
        }
    }
    CAmount nAmount             = 0;
    CAmount nPayFee             = 0;
    CAmount nAfterFee           = 0;
    CAmount nChange             = 0;
    unsigned int nBytes         = 0;
    unsigned int nBytesInputs   = 0;
    unsigned int nQuantity      = 0;
    bool fWitness               = false;
    std::vector<COutPoint> vCoinControl;
    coinControl()->ListSelected(vCoinControl);
    size_t i = 0;
    for (const auto& out : model->wallet().getCoins(vCoinControl)) {
        if (out.depth_in_main_chain < 0) continue;
        
        
        const COutPoint& outpt = vCoinControl[i++];
        if (out.is_spent)
        {
            coinControl()->UnSelect(outpt);
            continue;
        }