Since a few days ago (probably¹ [[https://www.mediawiki.org/wiki/MediaWiki_1.26/wmf6|1.26wmf6]]?), `added_lines` starts with a white space which is not present in the new wikitext of the page.
For example, on
https://pt.wikipedia.org/wiki/Special:AbuseLog/2162775?uselang=en
`mw.config.get('wgAbuseFilterVariables')['added_lines'][0][0] === " "`
returns `true` (in the JS console), but I didn't add any space before the "`#`" when I attempted to make that edit. Compare the values of `new_wikitext` and `added_lines`.
This is the source code of a filter which started to warn users incorrectly due to this regression:
https://pt.wikipedia.org/wiki/Special:AbuseFilter/59?uselang=en
There might be others filters broken out there, whose maintainers simply didn't notice (yet).
**Notes**
¹ This seems to be the first log with the problem on Portuguese Wikipedia:
https://pt.wikipedia.org/wiki/Special:AbuseLog/2156439?uselang=en