Index: /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIMachineView.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIMachineView.cpp	(revision 29991)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIMachineView.cpp	(revision 29992)
@@ -1081,5 +1081,7 @@
 
                 /* Check if we should activate window under cursor: */
-                if (machineWindowWrapper()->machineWindow() != QApplication::activeWindow())
+                if (QApplication::activeWindow() &&
+                    QApplication::activeWindow()->inherits("UIMachineWindow") &&
+                    QApplication::activeWindow() != machineWindowWrapper()->machineWindow())
                 {
                     /* Activating hovered machine window: */