I'm not sure how to make a bug out of this, but I want to note that nobody is taking advantage of the "tags" parameter on patrol actions, which will create ChangeTags. The API help makes it look like we should be specifying a tool or bot identity here, which might be useful, but a query shows that we never do so. The feature was added in January 2016.
SELECT * FROM wmf_raw.ApiAction WHERE year = 2018 AND month = 6 AND params['action'] = 'patrol' AND params['tags'] is not null ;
-> no rows selected.
I'd suggest either removing the feature or publicizing it better...