Neither web or the mobile site seems to truncate the title so not sure what "HN interface itself" you're referring to. Maybe you're using a third-part client?

Despite all my downvoters ... when you’re in single comment view the text most definitely is truncated on both desktop and mobile :).

That's absolutely true! Haven't noticed that before. I guess me and most people don't look for the title while responding to a comment.

Believe it or not, I generally find myself in these submissions based on viewing comments from https://news.ycombinator.com/newcomments . So yeah, just a bit jarring seeing so many people basically use the downvote button to call me a liar.