On cswiki, AbuseFilter tagged [an edit](https://cs.wikipedia.org/w/index.php?diff=12582567) as “removing a marker template” but in fact, the template was added just a little while prior to the edit, and the user probably did not have it in the original source code. After the save, the edit conflict caused by the added template was (probably) automerged and the article was OK afterwards.
But AbuseFilter tagged the change, as it apparently [saw the edit as “with template” -> “without template”](https://cs.wikipedia.org/wiki/Special:AbuseLog/185637), i.e. prior to the automerge. When you [examine the edit now, ex post](https://cs.wikipedia.org/wiki/Special:AbuseFilter/examine/18990150), you’ll see the edit differently, `old_wikitext` already includes the template, so `removed_lines` does not contain it.
The edit was made with VisualEditor, so I suspect it is involved in the problem.