2 files changed, 21 insertions, 0 deletions
diff --git a/src/gui/kernel/qwidget.cpp b/src/gui/kernel/qwidget.cpp
index 9b44f15..6c64ffc 100644
--- a/src/gui/kernel/qwidget.cpp
+++ b/src/gui/kernel/qwidget.cpp
@@ -236,6 +236,17 @@ void QWidgetBackingStoreTracker::unregisterWidget(QWidget *w)
     }
 }
 
+/*!
+    \internal
+    Recursively remove widget and all of its descendents.
+ */
+void QWidgetBackingStoreTracker::unregisterWidgetSubtree(QWidget *widget)
+{
+    unregisterWidget(widget);
+    foreach (QObject *child, widget->children())
+        if (QWidget *childWidget = qobject_cast<QWidget *>(child))
+            unregisterWidgetSubtree(childWidget);
+}
 
 QWidgetPrivate::QWidgetPrivate(int version)
     : QObjectPrivate(version)
@@ -10031,7 +10042,16 @@ void QWidget::setParent(QWidget *parent, Qt::WindowFlags f)
     if (newParent && isAncestorOf(focusWidget()))
         focusWidget()->clearFocus();
 
+    QTLWExtra *oldTopExtra = window()->d_func()->maybeTopData();
+    QWidgetBackingStoreTracker *oldBsTracker = oldTopExtra ? &oldTopExtra->backingStore : 0;
+
     d->setParent_sys(parent, f);
+
+    QTLWExtra *topExtra = window()->d_func()->maybeTopData();
+    QWidgetBackingStoreTracker *bsTracker = topExtra ? &topExtra->backingStore : 0;
+    if (oldBsTracker && oldBsTracker != bsTracker)
+        oldBsTracker->unregisterWidgetSubtree(this);
+
     if (desktopWidget)
         parent = 0;
 
diff --git a/src/gui/kernel/qwidget_p.h b/src/gui/kernel/qwidget_p.h
index 6c89659..ca1e3fc 100644
--- a/src/gui/kernel/qwidget_p.h
+++ b/src/gui/kernel/qwidget_p.h
@@ -122,6 +122,7 @@ public:
 
     void registerWidget(QWidget *w);
     void unregisterWidget(QWidget *w);
+    void unregisterWidgetSubtree(QWidget *w);
 
     inline QWidgetBackingStore* data()
     {