org export outcomes differ from one attempt to the next

[Eric S Fraga <e.fraga@ucl.ac.uk>]

Hello all,

I'm pulling my hair out in frustration...

I have a very large org file that comprises my lectures for a whole
course.  This org file makes extensive use of LaTeX and therefore has
quite a number of latex_header directives.

I have a very strange situation: if I start emacs, visit the file and
export to beamer LaTeX and then export again to beamer LaTeX, the result
of both exports differs. The difference is that some of the latex_header
lines do not get exported in the second attempt.

I have just verified this with "emacs -Q", loading in ox-latex and
ob-octave, then exporting, renaming the target out of the way and
exporting again.  A diff shows 3 lines in the first file that are not in
the second and 4 lines in the second that are not in the first.

What I've noticed, and which surprised me, is that the order of the
lines written out in the LaTeX preamble does not match the order of the
latex_header lines in my org file.

I cannot post a minimal example as any time I try to create one, the
problem disappears.  What I would like is some suggestion of how I can
track the problem down.  This problem has existed for quite some time
without me realising that there was a pattern to it.

Thanks,
eric

-- 
: Eric S Fraga (0xFFFCF67D), Emacs 25.0.50.2, Org release_8.3.1-234-g8c85c9