Steps to become confused:
- Open VisualEditor's wikitext mode, and paste in this content:
== Corrupted section == {{#lsth:}} == Innocent section == Plain section
- Try to save the page.
- Well, that didn't work, so switch to a different wikitext editor, paste it in there, and save it.
- Now open just the innocent section in VisualEditor's wikitext mode.
- Type a word or two.
- Try to save the page.
- Well, that didn't work either, which makes absolutely no sense if it's true section editing (i.e., not processing the rest of the page).
- File bug.
First spotted at https://www.mediawiki.org/wiki/Extension_talk:Labeled_Section_Transclusion and reported by @FreedomFighterSparrow at https://www.mediawiki.org/wiki/Topic:Tnmwzywj9gqgva8h