[O] Bug: Latex fragments: snippet-flag in packages alist ignored in 9.0.4

[plus]

Steps to reproduce:
1. emacs -Q
2. load org 9.0.4
3. (add-to-list 'org-latex-packages-alist '("" "polyglossia" nil))
4. switch to org-mode and attempt to render any fragment, e.g. $test$
5. error

If you look at the tex file produced, polyglossia has been included in
the preamble even though snippet-flag is nil. Additionally longtable,
wrapfig, rotating, capt-of, hyperref are all included in the preamble
despite the fact their snippet-flag is nil. (These are packages in
org-latex-default-packages-alist).

The relevant function that has been changed in 9.0.4 is
`org-create-formula-image'. It looks like the function used to generate
latex-header, `org-create-formula--latex-header', has been replaced with
`org-latex-make-preamble' (defined in ox-latex.el).

Restoring org-create-formula--latex-header from 9.0.3 and redefining
org-create-formula-image again restores the old behaviour for me. Of
course I don’t know what the problem actually is with the new function.

I should say I am not sure if this problem is specific to my
environment. Please let me know if you can reproduce it.

Emacs  : GNU Emacs 25.1.1 (x86_64-unknown-cygwin)
 of 2016-09-17
Package: Org mode version 9.0.4 (9.0.4-elpa @ 
/cygdrive/c/home/.emacs.d/elpa/org-20170124/)