Index: /trunk/src/VBox/Frontends/VirtualBox/src/platform/darwin/VBoxUtils-darwin-cocoa.mm
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/platform/darwin/VBoxUtils-darwin-cocoa.mm	(revision 50519)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/platform/darwin/VBoxUtils-darwin-cocoa.mm	(revision 50520)
@@ -38,4 +38,5 @@
 /** Easy way of dynamical call for 10.7 AppKit functionality we do not yet support. */
 #define NSWindowCollectionBehaviorFullScreenPrimary (1 << 7)
+#define NSFullScreenWindowMask (1 << 14)
 
 NativeNSWindowRef darwinToNativeWindowImpl(NativeNSViewRef pView)
@@ -201,4 +202,10 @@
     if ([pWindow respondsToSelector: @selector(toggleFullScreen:)])
         [pWindow performSelector: @selector(toggleFullScreen:) withObject: (id)nil];
+}
+
+bool darwinIsInFullscreenMode(NativeNSWindowRef pWindow)
+{
+    /* Check whether passed pWindow is in native fullscreen mode. */
+    return [pWindow styleMask] & NSFullScreenWindowMask;
 }
 
Index: /trunk/src/VBox/Frontends/VirtualBox/src/platform/darwin/VBoxUtils-darwin.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/platform/darwin/VBoxUtils-darwin.cpp	(revision 50519)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/platform/darwin/VBoxUtils-darwin.cpp	(revision 50520)
@@ -152,4 +152,9 @@
 {
     return ::darwinToggleFullscreenMode(::darwinToNativeWindow(pWidget));
+}
+
+bool darwinIsInFullscreenMode(QWidget *pWidget)
+{
+    return ::darwinIsInFullscreenMode(::darwinToNativeWindow(pWidget));
 }
 
Index: /trunk/src/VBox/Frontends/VirtualBox/src/platform/darwin/VBoxUtils-darwin.h
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/platform/darwin/VBoxUtils-darwin.h	(revision 50519)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/platform/darwin/VBoxUtils-darwin.h	(revision 50520)
@@ -82,4 +82,5 @@
 void darwinEnableTransienceSupport(NativeNSWindowRef pWindow);
 void darwinToggleFullscreenMode(NativeNSWindowRef pWindow);
+bool darwinIsInFullscreenMode(NativeNSWindowRef pWindow);
 bool darwinScreensHaveSeparateSpaces();
 
@@ -247,4 +248,5 @@
 void darwinEnableTransienceSupport(QWidget *pWidget);
 void darwinToggleFullscreenMode(QWidget *pWidget);
+bool darwinIsInFullscreenMode(QWidget *pWidget);
 bool darwinOpenFile(const QString &strFile);
 
Index: /trunk/src/VBox/Frontends/VirtualBox/src/runtime/fullscreen/UIMachineLogicFullscreen.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/runtime/fullscreen/UIMachineLogicFullscreen.cpp	(revision 50519)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/runtime/fullscreen/UIMachineLogicFullscreen.cpp	(revision 50520)
@@ -126,6 +126,14 @@
     Q_UNUSED(fResult);
 
-    /* Exit fullscreen mode if there is/are no fullscreen window(s) left: */
-    if (m_fullscreenMachineWindows.isEmpty())
+    /* If there is/are still fullscreen window(s) present: */
+    if (!m_fullscreenMachineWindows.isEmpty())
+    {
+        /* Ask remain window(s) to exit fullscreen too: */
+        foreach (UIMachineWindow *pMachineWindow, machineWindows())
+            if (darwinIsInFullscreenMode(pMachineWindow))
+                darwinToggleFullscreenMode(pMachineWindow);
+    }
+    /* If there is/are no more fullscreen window(s) left: */
+    else
     {
         /* Change visual-state to requested: */