Scrivener 2.1 (14118) breaks the MultiMarkdown 3 workflow for me, because
a) Exported Multimarkdown files always include
(it is desirable to have no metadata when using MultiMarkdown 3 if you want to generate a LaTeX-snippet)
and b) The first line of an exported .tex-file is always
(this has to be deleted by hand to make LaTeX typeset the file)
a) is undesirable in MultiMarkdown 3 because it makes it impossible to work with LaTeX snippets without postprocessing (see github.com/fletcher/peg-multimarkdown, section «“Complete” documents vs. “snippets”») and b) simply doesn’t create correct LaTeX-documents when using MultiMarkdown 3.
If there is no place in the settings I have missed, I consider this to be a bug. I haven’t tested with any other languages, but it would be nice if you could change Scrivener to allow exporting MultiMarkdown documents and «MultiMarkdown -> LaTeX» documents without any metadata.