Floating windows has an additional title bar partially visible

class CustomTitleBar : public QWidget
{
public:
    CustomTitleBar() : QWidget() {
        QHBoxLayout* layout = new QHBoxLayout(this);
        QPushButton* b = new QPushButton();
        b->setText(tr("New Button"));
        layout->addWidget(b, 1, Qt::AlignRight);
        layout->addSpacing(0);
        layout->setContentsMargins(QMargins());
    }
    
    virtual QSize minimumSizeHint() const
    {
        return QSize(30, 30);
    }
private:
protected:
};

DockWidgetPanel* panel1 = dockPanelManager()->addDockPanel(tr("Panel 1"), Qtitan::LeftDockPanelArea);
QWidget* anyWidget = new CustomTitleBar();
panel1->setTitleBar(anyWidget);