Index: /trunk/src/VBox/Main/xml/Settings.cpp
===================================================================
--- /trunk/src/VBox/Main/xml/Settings.cpp	(revision 35122)
+++ /trunk/src/VBox/Main/xml/Settings.cpp	(revision 35123)
@@ -1044,4 +1044,5 @@
         // no need to save the usual DVD medium types
         if (devType != DeviceType_DVD || (   mdm.hdType != MediumType_Normal
+                                          && mdm.hdType != MediumType_Writethrough
                                           && mdm.hdType != MediumType_Readonly))
             pelmMedium->setAttribute("type", pcszType);