REGRESSION: QPalette::setBrush does not reliably detach

diff --git a/examples/widgets/widgets/calculator/calculator.cpp b/examples/widgets/widgets/calculator/calculator.cpp
index 2c3669b7a8..691a4771ff 100644
--- a/examples/widgets/widgets/calculator/calculator.cpp
+++ b/examples/widgets/widgets/calculator/calculator.cpp
@@ -54,6 +54,7 @@
 #include <QGridLayout>
 #include <QLineEdit>
 #include <QtMath>
+#include <QEvent>
 
 //! [0]
 Calculator::Calculator(QWidget *parent)
@@ -140,6 +141,14 @@ Calculator::Calculator(QWidget *parent)
 }
 //! [6]
 
+bool Calculator::event(QEvent *e)
+{
+    if (e->type() == QEvent::PaletteChange) {
+        qDebug() << "palette changed. background" << palette().brush(QPalette::Window).color().rgba();
+    }
+    QWidget::event(e);
+}
+
 //! [7]
 void Calculator::digitClicked()
 {
diff --git a/examples/widgets/widgets/calculator/calculator.h b/examples/widgets/widgets/calculator/calculator.h
index 937de185e7..5082b32ef7 100644
--- a/examples/widgets/widgets/calculator/calculator.h
+++ b/examples/widgets/widgets/calculator/calculator.h
@@ -66,6 +66,7 @@ class Calculator : public QWidget
 public:
     Calculator(QWidget *parent = nullptr);
 
+    bool event(QEvent *) override;
 private slots:
     void digitClicked();
     void unaryOperatorClicked();
diff --git a/examples/widgets/widgets/calculator/main.cpp b/examples/widgets/widgets/calculator/main.cpp
index a034bb262e..cbfad39331 100644
--- a/examples/widgets/widgets/calculator/main.cpp
+++ b/examples/widgets/widgets/calculator/main.cpp
@@ -56,6 +56,12 @@ int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);
     Calculator calc;
+    QPalette p = calc.palette();
+    auto foo = p.brush(QPalette::Window);
+    // This changes QGuiApplication::app_pal because
+    // setBrush() does not detach (brush is the same as set),
+    // BUT it changes the resolve mask.
+    p.setBrush(QPalette::Window, foo);
     calc.show();
     return app.exec();
 }