- Edit a page that transcludes a template that provides a heading (e.g. https://www.mediawiki.org/w/index.php?title=Project:Sandbox&oldid=1886644&veaction=edit or https://wikitech.wikimedia.org/w/index.php?title=static.wikipedia.org&oldid=46977&veaction=edit)
- Put cursor in the "Insert paragraph" placeholder above this transclusion.
- Now Insert a template (e.g. template "Note" on mediawiki.org, or template "Doc-old" on wikitech)
- Observe how the preview looks (no issues)
- Save
Actual result:
Page renders as Note:==Heading== Content here. where the heading syntax is no longer parsed because it must be on a new line.
This is due to the template not being considered to be on its own line when the DOM is serialised by Parsoid.