Whilst working on the Reproducible Builds effort we noticed that gtk-doc generates unreproducible output.
There will likely be more issues but this one is at least fairly simple in that it iterates over a set structure when printing some .devhelp2 headers, for example:
│ │ │ │ - <sub name="Index of new API in 0.99.5" link="api-index-0-99-5.html"/>
│ │ │ │ - <sub name="Index of new API in 0.9.22" link="api-index-0-9-22.html"/>
│ │ │ │ <sub name="Index of new API in 0.9.0" link="api-index-0-9-0.html"/>
│ │ │ │ - <sub name="Index of new API in 0.9.1" link="api-index-0-9-1.html"/>
│ │ │ │ + <sub name="Index of new API in 0.9.19" link="api-index-0-9-19.html"/>
│ │ │ │ <sub name="Index of new API in 0.99.8" link="api-index-0-99-8.html"/>
│ │ │ │ + <sub name="Index of new API in 0.99.5" link="api-index-0-99-5.html"/>
│ │ │ │ <sub name="Index of new API in 1.0" link="api-index-1-0.html"/>
│ │ │ │ - <sub name="Index of new API in 0.9.19" link="api-index-0-9-19.html"/>
│ │ │ │ <sub name="Index of new API in 0.9.2" link="api-index-0-9-2.html"/>
│ │ │ │ + <sub name="Index of new API in 0.9.1" link="api-index-0-9-1.html"/>
│ │ │ │ + <sub name="Index of new API in 0.9.22" link="api-index-0-9-22.html"/>(This was originally filed in Debian as #946311.)