I just noticed that a "Possible duplicate of..." comment at https://gaming.stackexchange.com/questions/89421/if-i-want-to-be-a-normal-vampire-how-can-i-become-it-if-i-am-a-werewolf was automatically removed after I cast the last closing vote on it. I understand that this is to avoid redundancy, as the question will be automatically edited to include questions that it is a possible duplicate of, anyway.
However, my comment, "Also a possible duplicate of How exactly does lycanthropy work? Does it mix with vampirism?" wasn't auto-removed.
How does the auto-removal of these comments work? Do the comments have to follow a certain format so that they will get deleted? What other types of comments get an auto-delete?