[nem-en] About opening namespace

[vc]

   This code:
   
   using System;
   using SC = System.Collections;
   
   namespace X
   {
     using SC.Generic; // ERROR!
   
     module M
     {
       Main() : void
       {
         Console.WriteLine("");
       }
     }
   }
   
   report error:
   error : referenced namespace `SC.Generic' does not exist
   
   But, in C# similar code compile properly.
   
   It's a bug in compiler?