What the [bleep] is this?

Ok, I got a hold onto the "previews appear in wrong buffer" problem.
I just have no clue whatsoever what it is supposed to mean.

We have long ago solved that problem.  The code is here in preview.el:

(defadvice TeX-region-create (before preview-preamble preactivate)
  "Skip preamble for the sake of predumped formats."
[...]

So why doesn't it work anymore?  Because people are starting to use
the LaTeX toolbar (is that the only possible culprit?).  If I remove
the line

(add-hook 'LaTeX-mode-hook 'LaTeX-install-toolbar)

from my .emacs, everything works.  What has that to do with anything?
Try
C-h f TeX-region-create RET
in both cases.  When the LaTeX toolbar gets loaded in the above
manner, the advice is simply missing.  You can reactivate it using
ad-activate.

Can anybody figure out what the [bleep] is going on here?  I can't see
anything in tex-bar.el that would account for that, except maybe the
(require 'tex-buf), but what can _that_ have to do with it?

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum