QTableWidget separtion lines disappearing

[tuli]

Hi,

I have a perhaps somewhat unusual setup of a QTableWidget, where the tablewidget contains QLabels as cell-widgets, and those labels contain pixmaps to render something.
The problem: when I drag the columnsseparator to the left, the column separation line disappears.

I have created a simple example of the problem below. Just run it and play around with resizing the columns by dragging the header. Quickly the separation line will disappear. Screenshot:

h2wdjy5.png

code:

class mm : public QWidget
{
    Q_OBJECT
public:
    mm(QWidget* parent = nullptr) : QWidget(parent)
    {
        setFixedSize(500,500);
        table.setColumnCount(2);
        table.setRowCount(1);
        table.verticalHeader()->setStretchLastSection(true);
 
        table.setCellWidget(0, 0, l1 = new QLabel());
        table.setCellWidget(0, 1, l2 = new QLabel());
 
        auto l = new QHBoxLayout();
        l->addWidget(&table);
        setLayout(l);
    }
 
    QLabel *l1, *l2;
    QTableWidget table;
 
    void paintEvent(QPaintEvent* e) override
    {
        {
            QPixmap pm(l1->size());
            pm.fill(Qt::red);
            l1->setPixmap(pm);
        }
        {
            QPixmap pm(l2->size());
            pm.fill(Qt::black);
            l2->setPixmap(pm);
        }
    }
};

class mm : public QWidget
{
    Q_OBJECT
public:
    mm(QWidget* parent = nullptr) : QWidget(parent)
    {
        setFixedSize(500,500);
        table.setColumnCount(2);
        table.setRowCount(1);
        table.verticalHeader()->setStretchLastSection(true);

        table.setCellWidget(0, 0, l1 = new QLabel());
        table.setCellWidget(0, 1, l2 = new QLabel());

        auto l = new QHBoxLayout();
        l->addWidget(&table);
        setLayout(l);
    }

    QLabel *l1, *l2;
    QTableWidget table;

    void paintEvent(QPaintEvent* e) override
    {
        {
            QPixmap pm(l1->size());
            pm.fill(Qt::red);
            l1->setPixmap(pm);
        }
        {
            QPixmap pm(l2->size());
            pm.fill(Qt::black);
            l2->setPixmap(pm);
        }
    }
};

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Why does this happen and how can I ensure the lines are always drawn?

Happy Holidays!