Opengraph Metadata / flat arrays

I tried to adjust my opengraph metadata as described in the changelog of the 1.0.9 release.

[BC] Metadata now supports only flat arrays. To use open graph metas and the likes (ie, 'og:title'), simply specify it in the key.

These flat arrays do work for me in the site.yaml and site-wide.
If I use the same notation in the markdown headers, the site.yaml metadata is not overridden.
I tried a few variations, also mixing flat and non-flat arrays across both files but nothing seems to work.

It looks like the section in the docs (Opengraph-Metatag-Examples) has already been updated. So I tried that example too...without any luck.

metadata:
    'og:title': The Rock
    'og:type': video.movie
    'og:url': http://www.imdb.com/title/tt0117500/
    'og:image': http://ia.media-imdb.com/images/rock.jpg

Do I miss something?

Could be a bug. Open an issue on https://github.com/getgrav/grav so we don't lose track of it

here it is: https://github.com/getgrav/grav/issues/694

Thanks will look at this.