diff -r ddb02fd788ec -r 8731a1b81301 Hardware/Computer.cs
--- a/Hardware/Computer.cs	Tue Mar 15 22:00:31 2011 +0000
+++ b/Hardware/Computer.cs	Wed Mar 16 22:10:26 2011 +0000
@@ -268,9 +268,11 @@
       if (!open)
         return;
 
-      foreach (IGroup group in groups)
-        group.Close();
-      groups.Clear();
+      while (groups.Count > 0) {
+        IGroup group = groups[groups.Count - 1];
+        Remove(group);
+        group.Close(); 
+      } 
 
       Opcode.Close();
       Ring0.Close();