[O] org-mode html export background/foreground inconsistency

[lad]

I attempted to follow this blog to enable a background html export on
org file save: 

  http://stephanus-volke.de/posts/2015/Dez/22/org-mode-live-preview-en/

I tried adding the following to the top of the org file:

  # -*- after-save-hook: org-html-export-to-html;
  org-export-in-background: t; -*-

by the way I also tried:

  -*- after-save-hook: org-html-export-to-html;
  org-export-in-background: t; -*-
 
I even tried the following which I thought would work since I'm setting
the optional ASYNC variable to true:

  #-*- after-save-hook: (org-html-export-to-html t);
  org-export-in-background: t; -*-

For each test I tried I quit emacs and reopened to org file fresh. I was
prompted to accept some security settings and chose "y" so the variable
org-export-in-background is set correctly. The funny thing is when I go
through (C-c C-e h o) the export goes to the background, otherwise when
I save the file it happens in the foreground (which freezes emacs for
some time). :(

Running:
  
  Org-mode version 8.3.4 (8.3.4-50-g83e373-elpa)
  GNU Emacs 25.1.50.1

I'm not sure if this is correct behavior? Thank you in advance for any
insight or suggestions you may have.

- lad