I'm trying hard not to get too excited...but, after a few cursory tests, I agree, I think this is finally fixed.
But EVEN BETTER, this fix seems to have also actually fixed the problem with Outlook 2013 not displaying the BCC recipients in the copy of the sent message in the Sent Folder - a problem that is FAR older than this current fiasco with BCC!!
Examples:
Many of us were forced to "Save a copy" of the outgoing email in another local folder so that, after the message had been sent, we could review who had been BCC'd on that message - that was, of course, when we could still actually send BCC messages!
Like I say, I'm not holding my breath that either of these issues is truly and/or permanently fixed but maybe, just maybe, Microsoft finally fixed a problem.
Now perhaps they can turn their problem solvers to the issue of "This Outlook
2013 "The operation cannot be performed because the message has been changed" (many many years and 32 pages of appeals later!)