On AbuseFilter workboard we have a task, T58371, where a user noticed that the edit summary is different from what you would expect if you perform the edit by adding a new section. In fact, while in page history (and user contribs, etc.) the displayed summary is /* New_section_name */ something, AbuseFilter simply receives something as summary, without the comment. The reason is that EditFilterMergedContent hook omits the comment for new sections, and it's probably added after the hook is run. I don't know whether this is intentional and/or fixable, however it would be better to already have the comment inside the summary when the hook is run, to get a result which would be more similar to what users see.