Comment on Comments WordPress SEO Plugin by SEO Dave.
It used to be worse, Yoast also added the wrong canonical URL to the SEO comments on the original Prelovac version of the plugin. So even if you got the right title because Yoast set the wrong canonical, Google used to think it should only indexes the main post. I added a code fix, so that’s no longer an issue.
Yoast SEO isn’t a very good plugin, see Is Yoast the Best WordPress SEO Plugin?, don’t understand why webmasters use it in 2014.
I have a more advanced version of the SEO comments plugin built into Stallion Responsive (WordPress SEO package I develop) and because despite my recommendation not to use Yoast, Stallion users still use Yoast! I had to find fixes around the Yoast feck ups so Yoast wouldn’t replace the perfectly crafted Stallion SEO Super Comments title tags and canonical URLs. Basically had to build a different way to set a title tag so Yoast wouldn’t change it!
BTW I assumed you noticed how much better the output of the SEO comments are on this site. They have unique titles and the links to the comments use the titles as anchor text instead of the View Comment text.