My text editor (Kate) can put swap files on disk when a file is modified without being saved. sphinx-autobuild apparently thinks it has to rerun a build each time such a swap file is modified:
+--------- source/.index.rst.kate-swp changed -----------------------------------
| Running Sphinx v1.3.1
| loading pickled environment... done
| building [mo]: targets for 0 po files that are out of date
| building [html]: targets for 0 source files that are out of date
| updating environment: 0 added, 0 changed, 0 removed
| looking for now-outdated files... none found
| no targets are out of date.
| build succeeded.
+--------------------------------------------------------------------------------
My text editor (Kate) can put swap files on disk when a file is modified without being saved. sphinx-autobuild apparently thinks it has to rerun a build each time such a swap file is modified: