NIS interfering with Outlook selective-delete-from-server option

I use Outlook 2003 with Windows XP-SP3 for internet mail (Yahoo and Comcast). with the setting “Remove from server when deleted from “Deleted Items” (i.e., when permanently deleted from OL).  This Outlook setting has been working fine in tandem with NIS 2009, 2010, and -- up until recently -- 2011.

But lately something changed such that when I delete an open email (via File/Delete, the Delete icon, or Ctrl-D), Outlook seems to be *immediately* tagging the message as permanently deleted becuase it is being removed from the server even though it is actually still sitting in the Deleted Items folder.  The problem does NOT occur if I move the open message to the Deleted Items folder via a Move command instead.  It also does NOT occur if I close the message before deleting it to the Deleted Items folder (via any method).  But these alternate methods are less convenient for me, and have never been required in the past.

I have traced the issue to NIS. The same  problem is occurring on both of my NIS installations.  Although turning off Norton email protection does not change anything, upon completely uninstalling Norton Outlook stops "jumping the gun" on the message deletions from the server.  But once I reinstall NIS, the problem returns.

Any advice on a way around this odd and annoying bug?  Again, everything worked properly until recently.  Was there recently a silent NIS program update that may have caused the issue?  I have NIS 2011 18.6.0.29.  Thanks.