1 files changed, 6 insertions, 4 deletions
diff --git a/src/widgets/widgets/qmdisubwindow.cpp b/src/widgets/widgets/qmdisubwindow.cpp
index 14aeb73baf..0f38eee6cd 100644
--- a/src/widgets/widgets/qmdisubwindow.cpp
+++ b/src/widgets/widgets/qmdisubwindow.cpp
@@ -1000,7 +1000,9 @@ void QMdiSubWindowPrivate::removeBaseWidget()
         q->setWindowModified(false);
     }
     lastChildWindowTitle.clear();
-    baseWidget->setParent(0);
+    // QTBUG-47993: parent widget can be reset before this call
+    if (baseWidget->parentWidget() == q)
+        baseWidget->setParent(0);
     baseWidget = 0;
     isWidgetHiddenByUs = false;
 }
@@ -2307,7 +2309,7 @@ void QMdiSubWindow::setWidget(QWidget *widget)
         return;
     }
 
-    if (widget == d->baseWidget) {
+    if (Q_UNLIKELY(widget == d->baseWidget)) {
         qWarning("QMdiSubWindow::setWidget: widget is already set");
         return;
     }
@@ -2505,7 +2507,7 @@ void QMdiSubWindow::setKeyboardPageStep(int step)
 void QMdiSubWindow::setSystemMenu(QMenu *systemMenu)
 {
     Q_D(QMdiSubWindow);
-    if (systemMenu && systemMenu == d->systemMenu) {
+    if (Q_UNLIKELY(systemMenu && systemMenu == d->systemMenu)) {
         qWarning("QMdiSubWindow::setSystemMenu: system menu is already set");
         return;
     }
@@ -2653,7 +2655,7 @@ void QMdiSubWindow::showShaded()
     resize(d->internalMinimumSize);
 
     // Hide the internal widget if not already hidden by the user.
-    if (d->baseWidget && !d->baseWidget->isHidden()) {
+    if (d->baseWidget && !d->baseWidget->isHidden() && !(windowFlags() & Qt::FramelessWindowHint)) {
         d->baseWidget->hide();
         d->isWidgetHiddenByUs = true;
     }