#include <QApplication>

#include <QMainWindow>
#include <QTabWidget>
#include <QAction>
#include <QMenuBar>
#include <QHBoxLayout>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    auto w = new QMainWindow();
    w->setMinimumSize({ 300, 300 });
    w->show();

    auto c = new QWidget();
    auto l = new QHBoxLayout();
    c->setLayout(l);
    w->setCentralWidget(c);

    auto tw1 = new QTabWidget();
    l->addWidget(tw1);

    auto addTab = [tw1](const QString& title)
    {
        auto tab = new QWidget(tw1);
        tab->setStyleSheet("background-color: red");
        tab->setMinimumSize({ 200, 200 });
        tw1->addTab(tab, title);

        tab->setAttribute(Qt::WA_NativeWindow);
    };

    addTab("tab 1");
    addTab("tab 2");
    addTab("tab 3");
    addTab("tab 4");

    auto mb = w->menuBar();

    auto action = new QAction("Move to new tab widget", w);
    QObject::connect(action, &QAction::triggered, w, [tw1, l, c]() {

        auto tw2 = new QTabWidget(c);

        // showing the tab widget before inserting the tab prevents the issue
        //tw2->show();

        l->addWidget(tw2);

        auto t1 = tw1->widget(0);
        tw1->removeTab(0);

        // reparenting before inserting prevents the issue
        //t1->setParent(tw2);

        tw2->addTab(t1, "tab");
    });

    mb->addAction(action);

    return a.exec();
}