I was doing a review, and came across a Very Low Quality answer that I was going to recommend for deletion, but only after leaving a detailed comment to help the poster learn for the future. I typed up the comment, then was greeted with the infamous
You cannot comment on deleted/locked posts message. Since this was in the Review Queue, obviously it was an audit to make sure I wasn't robo-reviewing, and I clicked on the Delete (no comment) button.
Of course, I passed. I feel this is a bug since anyone could just copy and paste a 15-character message into the Comment field, and determine if the post was deleted. I'd suggest making it "look" like the comment was added, to help make audits a little more challenging.