https://bugs.gentoo.org/959225
https://bugreports.qt.io/browse/QTBUG-137755
https://codereview.qt-project.org/c/qt/qtbase/+/653890
https://codereview.qt-project.org/c/qt/qtbase/+/653891
https://codereview.qt-project.org/c/qt/qtbase/+/653892
https://codereview.qt-project.org/c/qt/qtbase/+/653893
https://codereview.qt-project.org/c/qt/qtbase/+/653894
--- a/src/widgets/widgets/qmainwindowlayout.cpp
+++ b/src/widgets/widgets/qmainwindowlayout.cpp
@@ -1768,6 +1768,4 @@
     for (QTabBar *bar : std::as_const(usedTabBars))
         bar->setDocumentMode(_documentMode);
-    for (QTabBar *bar : std::as_const(unusedTabBars))
-        bar->setDocumentMode(_documentMode);
 }
 
@@ -1894,5 +1892,5 @@
 {
     Q_OBJECT
-    QMainWindow *mainWindow;
+    QPointer<QMainWindow> mainWindow;
     QPointer<QDockWidget> draggingDock; // Currently dragging (detached) dock widget
 public:
@@ -1909,4 +1907,20 @@
 };
 
+QDebug operator<<(QDebug debug, const QMainWindowTabBar *bar)
+{
+    if (!bar)
+        return debug << "QMainWindowTabBar(0x0)";
+    QDebugStateSaver saver(debug);
+    debug.nospace().noquote() << "QMainWindowTabBar(" << static_cast<const void *>(bar) << ", ";
+    debug.nospace().noquote() << "ParentWidget=(" << bar->parentWidget() << "), ";
+    const auto dockWidgets = bar->dockWidgets();
+    if (dockWidgets.isEmpty())
+        debug.nospace().noquote() << "No QDockWidgets";
+    else
+        debug.nospace().noquote() << "DockWidgets(" << dockWidgets << ")";
+    debug.nospace().noquote() << ")";
+    return debug;
+}
+
 QMainWindowTabBar *QMainWindowLayout::findTabBar(const QDockWidget *dockWidget) const
 {
@@ -1954,5 +1968,5 @@
     QMainWindowTabBar *that = const_cast<QMainWindowTabBar *>(this);
     QMainWindowLayout* mlayout = qt_mainwindow_layout(mainWindow);
-    QDockAreaLayoutInfo *info = mlayout->dockInfo(that);
+    QDockAreaLayoutInfo *info = mlayout ? mlayout->dockInfo(that) : nullptr;
     if (!info)
         return nullptr;
@@ -2049,5 +2063,4 @@
     if (!mwLayout)
         return;
-    mwLayout->unusedTabBars.removeOne(this);
     mwLayout->usedTabBars.remove(this);
 }
@@ -2105,4 +2118,10 @@
 }
 
+void QMainWindowLayout::unuseTabBar(QTabBar *bar)
+{
+    Q_ASSERT(qobject_cast<QMainWindowTabBar *>(bar));
+    delete bar;
+}
+
 QTabBar *QMainWindowLayout::getTabBar()
 {
@@ -2116,19 +2135,14 @@
     }
 
-    QTabBar *result = nullptr;
-    if (!unusedTabBars.isEmpty()) {
-        result = unusedTabBars.takeLast();
-    } else {
-        result = new QMainWindowTabBar(static_cast<QMainWindow *>(parentWidget()));
-        result->setDrawBase(true);
-        result->setElideMode(Qt::ElideRight);
-        result->setDocumentMode(_documentMode);
-        result->setMovable(true);
-        connect(result, SIGNAL(currentChanged(int)), this, SLOT(tabChanged()));
-        connect(result, &QTabBar::tabMoved, this, &QMainWindowLayout::tabMoved);
-    }
+    QTabBar *bar = new QMainWindowTabBar(static_cast<QMainWindow *>(parentWidget()));
+    bar->setDrawBase(true);
+    bar->setElideMode(Qt::ElideRight);
+    bar->setDocumentMode(_documentMode);
+    bar->setMovable(true);
+    connect(bar, SIGNAL(currentChanged(int)), this, SLOT(tabChanged()));
+    connect(bar, &QTabBar::tabMoved, this, &QMainWindowLayout::tabMoved);
 
-    usedTabBars.insert(result);
-    return result;
+    usedTabBars.insert(bar);
+    return bar;
 }
 
@@ -2731,12 +2745,4 @@
 
     delete statusbar;
-
-#if QT_CONFIG(dockwidget) && QT_CONFIG(tabwidget)
-    // unusedTabBars contains unparented tab bars, which need to be removed manually.
-    // ~QMainWindowTabBar() attempts to remove the bar from unusedTabBars
-    // => move it out of the way first.
-    const auto bars = std::move(unusedTabBars);
-    qDeleteAll(bars);
-#endif // QT_CONFIG(dockwidget) && QT_CONFIG(tabwidget)
 }
 
@@ -3213,8 +3219,5 @@
     usedTabBars = used;
     for (QTabBar *tab_bar : retired) {
-        tab_bar->hide();
-        while (tab_bar->count() > 0)
-            tab_bar->removeTab(0);
-        unusedTabBars.append(tab_bar);
+        unuseTabBar(tab_bar);
     }
 
--- a/src/widgets/widgets/qmainwindowlayout_p.h
+++ b/src/widgets/widgets/qmainwindowlayout_p.h
@@ -551,6 +551,6 @@
 
     QTabBar *getTabBar();
+    void unuseTabBar(QTabBar *bar);
     QSet<QTabBar*> usedTabBars;
-    QList<QTabBar*> unusedTabBars;
     bool verticalTabsEnabled;