I see that `legacy` means `P2PKH` in both command line options and RPC help info:
```
-addresstype
What type of addresses to use ("legacy", "p2sh-segwit", or "bech32", default: "p2sh-segwit") 
```
```
getnewaddress ( "label" "address_type" )
...
2. address_type    (string, optional, default=set by -addresstype) The address type to use. Options are "legacy", "p2sh-segwit", and "bech32".
...
```

The useLegacyAddress checkbox describes itself as “Generate legacy address” - however, it actually makes the wallet GUI generate “p2sh-segwit” address for the user if it's checked.
{
    delete ui;
}
void ReceiveCoinsDialog::clear()
{
    ui->reqAmount->clear();
    ui->reqLabel->setText("");
    ui->reqMessage->setText("");
    updateDisplayUnit();
}
void ReceiveCoinsDialog::reject()
{
    clear();
}
void ReceiveCoinsDialog::accept()
{
    clear();
}
void ReceiveCoinsDialog::updateDisplayUnit()
{
    if(model && model->getOptionsModel())
    {
        ui->reqAmount->setDisplayUnit(model->getOptionsModel()->getDisplayUnit());
    }
}
void ReceiveCoinsDialog::on_receiveButton_clicked()