Index: /trunk/src/VBox/Frontends/VirtualBox/src/widgets/VBoxMiniToolBar.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/widgets/VBoxMiniToolBar.cpp	(revision 35866)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/widgets/VBoxMiniToolBar.cpp	(revision 35867)
@@ -260,4 +260,10 @@
     if (pEvent->timerId() == m_scrollTimer.timerId())
     {
+        /* Due to X11 async nature, this timer-event could come before parent
+         * VM window become visible, we should ignore those timer-events: */
+        if (QApplication::desktop()->screenNumber(window()) == -1)
+            return;
+
+        /* Update tool-bar position: */
         QRect screen = m_fSeamless ? vboxGlobal().availableGeometry(QApplication::desktop()->screenNumber(window())) :
                                      QApplication::desktop()->screenGeometry(window());