Imported metafile in PPT shows wrong font kerning

I’m running Libreoffice on Ubuntu 14.04. I’ve imported a PPT from an external source into Impress and noticed that the embedded diagrams in that PPT show some broken kerning (characters overlapping etc.). I’ve tried various font substitutions, but they don’t seem to apply to metafiles.

Consequently, I’d like to either…
* edit the embedded metafiles directly or
* somehow swap out the used font.

Note that I haven’t been able to actually find out what font the metafiles use, if I select it, I only get “Metafile object” as information.