Index: /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIFrameBufferQuartz2D.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIFrameBufferQuartz2D.cpp	(revision 43759)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIFrameBufferQuartz2D.cpp	(revision 43760)
@@ -435,4 +435,13 @@
     else
     {
+        /* Main (IDisplay) sending guest resize-event thinks that
+         * width and/or height can be zero (0) if this frame-buffer is hidden,
+         * we should just do a fallback to initial blackout
+         * frame-buffer of 640x480 size (like we are doing for QImage frame-buffer): */
+        if (m_width == 0 || m_height == 0)
+        {
+            m_width = 640;
+            m_height = 480;
+        }
         m_fUsesGuestVRAM = false;
         remind = true;
Index: /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIMachineView.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIMachineView.cpp	(revision 43759)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIMachineView.cpp	(revision 43760)
@@ -918,8 +918,4 @@
         return true;
 
-    /* We should not process resize-event if parent window is hidden: */
-    if (!uisession()->isScreenVisible(m_uScreenId))
-        return true;
-
     /* Get guest resize-event: */
     UIResizeEvent *pResizeEvent = static_cast<UIResizeEvent*>(pEvent);