Render Preset Copy Misbehaving

While rendering I wanted to tweak some settings but the output looked like a horribly compressed jpeg slideshow.
The Preset being copied: WebM-VP8/Vorbis (libre)
Out of concern that I don’t know what I am doing I ran a test by saving the current default and rendering with the new copy before tweaking anything. It still looks like a mess. Is there a way for me to inspect the default preset to perhaps copy it manually? Are the custom presets bugged?