A user just posted his question a second time here on meta after the first was closed as a duplicate. I wrote a comment on the second post, explaining that the answer to his question is in the linked duplicate and that he shouldn't circumvent the closure process by asking a second identical question.
When the second post was closed as a duplicate my comment was automatically deleted. As far as I understand this is a heuristic that removes obsolete comments, which it considers every comment that contains a link to one of the duplicates.
This heuristic is too aggressive and removes comments that go beyond "Duplicate here: link". I suggest that it should be changed to only remove the default duplicate comment, and not any comment that was edited by the owner nor any free-form comment that happens to include a link to the duplicate.
This also triggers for any comment that contains the word "duplicate" and link to any question, not only the question being chosen as duplicate, which makes this much worse.