Why systems won't be removed from Red Hat Satellite 5.6 after upgrade?

Issue

• Why systems won't be removed from Red Hat Satellite 5.6 after upgrade?

• After upgrading satellite to version 5.6, deleting all the inactive systems using webui, spacecmd or delete-old-systems-interactive command won't work even though result says success:

  # delete-old-systems-interactive --idle 4d
  Total systems [2649], will delete [2649]
  All systems deleted
  
  # spacecmd system_delete
  
  From webui:
  => Systems => Manage=> Misc=> Delete System Profiles=> Confirm Deletion
  Result: "The selected systems in the System Set Manager have been queued for deletion." Server Deletion  : Status completed.
  

  However the systems still exists on the Web GUI.