2 files changed, 32 insertions, 1 deletions
diff --git a/src/gui/painting/qbackingstore.cpp b/src/gui/painting/qbackingstore.cpp
index 0f7933c..3bbdf7f 100644
--- a/src/gui/painting/qbackingstore.cpp
+++ b/src/gui/painting/qbackingstore.cpp
@@ -258,7 +258,10 @@ void QWidgetBackingStore::unflushPaint(QWidget *widget, const QRegion &rgn)
 bool QWidgetBackingStore::bltRect(const QRect &rect, int dx, int dy, QWidget *widget)
 {
     const QPoint pos(tlwOffset + widget->mapTo(tlw, rect.topLeft()));
-    return windowSurface->scroll(QRect(pos, rect.size()), dx, dy);
+    const QRect tlwRect(QRect(pos, rect.size()));
+    if (dirty.intersects(tlwRect))
+        return false; // We don't want to scroll junk.
+    return windowSurface->scroll(tlwRect, dx, dy);
 }
 
 void QWidgetBackingStore::releaseBuffer()
diff --git a/tests/auto/qwidget/tst_qwidget.cpp b/tests/auto/qwidget/tst_qwidget.cpp
index a6458a5..e65fef1 100644
--- a/tests/auto/qwidget/tst_qwidget.cpp
+++ b/tests/auto/qwidget/tst_qwidget.cpp
@@ -252,6 +252,7 @@ private slots:
 
     void moveChild_data();
     void moveChild();
+    void showAndMoveChild();
 
     void subtractOpaqueSiblings();
 
@@ -5303,6 +5304,33 @@ void tst_QWidget::moveChild()
                  parent.color);
 }
 
+void tst_QWidget::showAndMoveChild()
+{
+    QWidget parent(0, Qt::FramelessWindowHint);
+    parent.resize(300, 300);
+    parent.setPalette(Qt::red);
+    parent.show();
+#ifdef Q_WS_X11
+    qt_x11_wait_for_window_manager(&parent);
+#endif
+    QTest::qWait(200);
+
+    const QPoint tlwOffset = parent.geometry().topLeft();
+    QWidget child(&parent);
+    child.resize(100, 100);
+    child.setPalette(Qt::blue);
+    child.setAutoFillBackground(true);
+
+    // Ensure that the child is repainted correctly when moved right after show.
+    // NB! Do NOT processEvents() (or qWait()) in between show() and move().
+    child.show();
+    child.move(150, 150);
+    qApp->processEvents();
+
+    VERIFY_COLOR(child.geometry().translated(tlwOffset), Qt::blue);
+    VERIFY_COLOR(QRegion(parent.geometry()) - child.geometry().translated(tlwOffset), Qt::red);
+}
+
 void tst_QWidget::subtractOpaqueSiblings()
 {
 #ifdef QT_MAC_USE_COCOA