QTreeView Stylesheet: alternate-background-color ignored (QT-5.2.1)

I have created a very simple application using the Qt Creator (basically a main window with a QTreeView inside + a couple rows).
It runs fine except the alternate-background-color is totally ignored.

Attachment 10275

Here's the code. I also tried putting the style sheet using the QT Designer but it didn't make a difference.
Can anyone tell me what's wrong?

Code:

const char *STYLE_SHEET =
        "QTreeView"
        "{"
           "color: #000000;"
           "background-color: #B6B6B6;"
           "alternate-background-color: #FFFFFF;"
           "selection-color: #FF0000;"
           "selection-background-color: #7FB3E6;"
        "}";
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    a.setStyleSheet(STYLE_SHEET);
    QStandardItemModel m;
    QStandardItem *root = m.invisibleRootItem();
    root->appendRow(new QStandardItem("1"));
    root->appendRow(new QStandardItem("2"));
    root->appendRow(new QStandardItem("3"));
    MainWindow w(&m);
    w.show();
    return a.exec();
}

Code:

MainWindow::MainWindow(QStandardItemModel *m, QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
 
    ui->treeView->setModel(m);
    ui->treeView->expandAll();
}

I am using QT-5.2.1 under Mac OS X Mavericks.

Thanks!