Index: /trunk/src/VBox/Main/src-server/SnapshotImpl.cpp
===================================================================
--- /trunk/src/VBox/Main/src-server/SnapshotImpl.cpp	(revision 64211)
+++ /trunk/src/VBox/Main/src-server/SnapshotImpl.cpp	(revision 64212)
@@ -3127,5 +3127,10 @@
 
             if (fNeedSourceUninit)
+            {
+                // make sure that the diff image to be deleted has no parent,
+                // even in error cases (where the deparenting may be missing)
+                it->mpSource->i_deparent();
                 it->mpSource->uninit();
+            }
 
             // One attachment is merged, must save the settings