Understanding docs have duplicate "Test rules" in page content section

As the title says ... for understanding docs that have a "Test rules" 
heading, there is then always a duplicate second "Test rules" link in 
the right-hand "Page content" box-out.

Examples:

* 
https://w3c.github.io/wcag/understanding/audio-only-and-video-only-prerecorded
* https://w3c.github.io/wcag/understanding/captions-prerecorded
* 
https://w3c.github.io/wcag/understanding/audio-description-or-media-alternative-prerecorded
* https://w3c.github.io/wcag/understanding/audio-description-prerecorded
* https://w3c.github.io/wcag/understanding/media-alternative-prerecorded

I assume this is part of some broken page building logic.

(Also noting that the styles are still broken for those understanding 
documents served from github.io, with the "Skip to content" link always 
visible, and some of the image-related styles not present)

-- 
Patrick H. Lauke

https://www.splintered.co.uk/ | https://github.com/patrickhlauke
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