Verify desktop widget screen number before applying size changes

This resolves Bug 1378

src/kernel/qapplication_x11.cpp

@@ -3472,13 +3472,26 @@ int QApplication::x11ProcessEvent( XEvent* event )
 	// update the size for desktop widget
 	int scr = XRRRootToScreen( appDpy, event->xany.window );
 	QWidget *w = desktop()->screen( scr );
-	QSize oldSize( w->size() );
-	w->crect.setWidth( DisplayWidth( appDpy, scr ) );
-        w->crect.setHeight( DisplayHeight( appDpy, scr ) );
-	if ( w->size() != oldSize ) {
-	    QResizeEvent e( w->size(), oldSize );
-	    QApplication::sendEvent( w, &e );
-	    emit desktop()->resized( scr );
+
+	if (w) {
+	    int widgetScr = -1;
+	    // make sure the specified widget is on the same screen that received the XRandR event
+	    XWindowAttributes widgetAttr;
+	    XGetWindowAttributes(appDpy, w->winId(), &widgetAttr);
+	    if (widgetAttr.screen) {
+		widgetScr = XScreenNumberOfScreen(widgetAttr.screen);
+	    }
+
+	    if ((widgetScr < 0) || (widgetScr == scr)) {
+		QSize oldSize( w->size() );
+		w->crect.setWidth( DisplayWidth( appDpy, scr ) );
+		w->crect.setHeight( DisplayHeight( appDpy, scr ) );
+		if ( w->size() != oldSize ) {
+		QResizeEvent e( w->size(), oldSize );
+		QApplication::sendEvent( w, &e );
+		    emit desktop()->resized( scr );
+		}
+	    }
 	}
     }
 #endif // QT_NO_XRANDR