sphinx_build: index.rst changes should force rebuilding every html file

Problem

index.rst changes should force rebuilding every html file since the short table of contents is included in every html, but the incremental sphinx-build doesn't check this dependency. (Hope this is enough detail since I'm not the one who set up sphinx for my project; I'm just trying to write documentation today.)

Procedure to reproduce the problem

original index.rst is (in part):

.. toctree::
   :caption: Preamble

   self
   introduction
   credits
   license

1. Complete a successful sphinx-build.
2. Move the license entry before the credits entry in index.rst.
3. Repeat sphinx-build

Results

Files other than index.html show the incorrect (original) order rather than the changed order:

Expected results

All html files should show the correct (changed) order, which only appears in index.html:

Error logs

COQBIN="/cygdrive/c/Users/Jim.DESKTOP-MMPNVGH/Documents/coqSource/coq/bin/" sphinx-build -b html \
        -d doc/sphinx/_build/doctrees -j4 doc/sphinx doc/sphinx/_build/html
Running Sphinx v1.7.7
loading pickled environment... done
Skipping /cygdrive/c/Users/Jim.DESKTOP-MMPNVGH/Documents/coqSource/coq/doc/sphinx/credits.html.rst: /cygdrive/c/Users/Jim.DESKTOP-MMPNVGH/Documents/coqSource/coq/doc/sphinx/credits.rst is up to date
Copying /cygdrive/c/Users/Jim.DESKTOP-MMPNVGH/Documents/coqSource/coq/doc/sphinx/index.html.rst to /cygdrive/c/Users/Jim.DESKTOP-MMPNVGH/Documents/coqSource/coq/doc/sphinx/index.rst
Skipping /cygdrive/c/Users/Jim.DESKTOP-MMPNVGH/Documents/coqSource/coq/doc/sphinx/zebibliography.html.rst: /cygdrive/c/Users/Jim.DESKTOP-MMPNVGH/Documents/coqSource/coq/doc/sphinx/zebibliography.rst is up to date
building [mo]: targets for 0 po files that are out of date
building [html]: targets for 1 source files that are out of date
updating environment: 0 added, 1 changed, 0 removed
reading sources... [100%] index

looking for now-outdated files... none found
pickling environment... done
checking consistency... done
preparing documents... done
waiting for workers...
generating indices... genindex coq-cmdindex coq-tacindex coq-optindex coq-exnindex
writing additional pages... search
copying static files... done
copying extra files... done
dumping search index in English (code: en) ... done
dumping object inventory... done
build succeeded.

Environment info

• OS: Windows
• Python version: 3.6.5
• Sphinx version: 1.7.7
• <Extra tools e.g.: Browser, tex or something else>

Start by reproducing the issue with the shown index.rst toctree and incremental sphinx-build command on Sphinx 1.7.7. Trace how the changed index.rst is recorded and how dependent HTML documents are selected for rebuilding. Done means reordering entries causes every affected HTML file to show the new table-of-contents order.