Index: /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIMouseHandler.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIMouseHandler.cpp	(revision 30910)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIMouseHandler.cpp	(revision 30911)
@@ -574,4 +574,8 @@
                                 int wheelDelta, Qt::Orientation wheelDirection)
 {
+    /* Check if machine is still running: */
+    if (!uisession()->isRunning())
+        return true;
+
     /* Check if such view & viewport are registered: */
     if (!m_views.contains(uScreenId) || !m_viewports.contains(uScreenId))