What I meant is why the URLs in the first post don’t render anything (they also have proper <title> attribute) whereas the URL in my comment above did render a title. I have found a pattern, and now I don’t know whether this is a bug or a feature working as designed.
Here goes a test showing the difference:
A task (URL in new line right below)
https://phabricator.wikimedia.org/T180854
A task (URL in new line with an empty line in between)
https://phabricator.wikimedia.org/T180854
(URL in one line preceded by anything, some text, a blank space)
A task: ⚓ T180854 Create discourse-mediawiki.wmflabs.org (pilot instance)
⚓ T180854 Create discourse-mediawiki.wmflabs.org (pilot instance)