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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.

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Agreed. For a long time I thought that even edited auto comments were not deleted, but then when wondering about the same, I read Jeff's answer: "If you don't want the comment deleted, make sure it doesn't begin with "possible duplicate of". – Arjan Jul 27 '12 at 16:53
@Arjan I don't think I put that in front, I wrote the comment first and then voted to close as duplicate. I think the heuristic is even more aggressive than Jeff says. – Mad Scientist Jul 27 '12 at 16:56
Yeah, sorry, I just edited "even" and "auto" into my comment. I fully agree with what you're asking, and I think I've seen what you're describing too. But then: I often question my own memory ;-) – Arjan Jul 27 '12 at 16:58
Same happened to me here, where I did not vote to close, but did post a comment that linked to what became the duplicate. I did use the word "duplicate" though. – Arjan Aug 2 '12 at 18:46
Ah, it seems this has changed: even an edited "possible duplicate" auto-comment was not deleted here. (screenshot) Though elsewhere a manual comment (screenshot before, after) was deleted, but maybe by its author. – Arjan Aug 12 '12 at 15:37
Ah, the author of the 2nd comment confirmed it was deleted manually. So, it seems things are resolved indeed. – Arjan Aug 12 '12 at 16:47
Twice in the past few days I've seen my customized comments removed that just happened to contain a link to the duplicate. Just now, I had composed the comment first, Yadda yadda yadda. This is [a duplicate](link://to.duplicate). And so on and so forth. and then voted to close. The comment no longer exists, although it had other information which is referred to further along in the thread. This is broken, either again or still. The more recent one was immediately before this comment. – Josh Caswell Dec 18 '12 at 21:06
@Josh, it seems this was fixed. That is: even an auto-comment of mine was left untouched when a question was closed, so I assume manual comments are no longer deleted either. – Arjan Jan 13 '13 at 21:47
It might still only apply to edited comments. (Which is fine for this feature request, but might not solve the issue @Josh and myself were seeing earlier with our own comments that also happened to reference the same duplicate post.) – Arjan Jan 14 '13 at 18:31
And @Josh commented Jan 27 on my deleted answer: Not sure what's going on, but I've once again had an edited "possible duplicate of <auto-inserted-link>, <link I added>, <link I added>, <link I added>" comment deleted just now. This seems to just be a buggy situation to me. Comment was here: (I've manually re-posted the other links.) – Arjan Feb 6 '13 at 20:43
I swear this keeps bouncing back and forth between happening and not happening. This week, it is, and it's driving me nuts. – Josh Caswell May 15 '13 at 19:45
Today, I started a question that seemed to be a duplicate of this one, har har. I don't understand why anyone would even want the comments to be removed. Do we remove comments requiring clarification after the question was edited? Do they take up too much database space? Is a comment containing a link that is later edited into the question ... duplicate? – CodeCaster Jul 10 '13 at 19:12
For reference: in April 2010 Jeff wrote If you don't want the comment deleted, make sure it doesn't begin with "possible duplicate of" and also OK, the "possible duplicate of..." comments are only deleted now in the case where the question was closed as a duplicate. They are also not deleted if they have a non-null EditCount (that is, the little pencil icon). – Arjan Jul 22 '13 at 6:34
Ah, just had a 100% manual comment deleted again (here). It included two URLs, one of which I also used to vote to close after posting that comment. It did not hold the text "possible duplicate of", but did include the word "duplicate". (I even made a screenshot, but was stupid enough to have lost that when the question was eventually closed. One can still see the other URL in the linked section though.) – Arjan Jul 23 '13 at 11:42
And again I'm not sure about myself, or I'm seeing the same randomness @Josh reported. My previous comment was backed by the other URL still being shown in the linked section (not anymore right now). And meanwhile a developer has confirmed that my comment was deleted by Community upon closure. But: not so much in another question which I voted to close today, where my 100% manual (upvoted & edited) comment is still there after closure... – Arjan Jul 23 '13 at 16:24
up vote 30 down vote

To merge something else in here; it's worse than you describe. Any comment that contains the word "duplicate" and a link to another question is deleted when a question is closed. This might be solely comments that are owned by someone who voted but I'm unable to test.

It doesn't matter if the comment is anything to do with any of the questions that the question in question is being closed as a duplicate of. Flexo's comment to Does voting to close as duplicate erase earlier comments? would indicate that this has been happening for a while.

I had two comments on Subtract boolean from float in python deleted. One was an unmodified auto-generated possible duplicate comment. The other indicated a potential alternate duplicate; something along the lines of:

A better duplicate might be Is it guaranteed that False “is 0” and True “is 1”? but it was closed as a duplicate of the first question

I've done some science. It seems that the word "duplicate" is not enough; I wrote "duplicate test comment" on java.concurrent.ReentrantLock - why we want to acquire the same lock multiple times but it didn't get deleted (I did it manually).

However, on I wrote "possible duplicate test comment [test](some question)", this comment was deleted.

This shouldn't happen. Comments pointing out separate linkages can be incredibly useful and make the web1 a better place.

1. Pun intended; please tell me someone noticed ;-)?

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I noticed........after I read there was a pun. – Cole Johnson Sep 3 '13 at 23:31
It's flaky like the county fair's blue ribbon pie crust. Thanks for doing some deliberate testing. – Josh Caswell Sep 4 '13 at 8:01
Yep, just happened to me too here. I did NOT vote to close. – Arjan Oct 21 '13 at 14:26
And happened to me here. It contained the phrase "possible duplicate" but only in the context "I don't think any of the solutions in the possible duplicate will work for you" – Martin Smith Oct 21 '13 at 14:31
And here I added the "possible duplicate" comment myself, after I voted, as none appeared after my vote. Maybe someone voted earlier, and retracted and undid their close vote? I guess when the 5th close vote is cast, my manual comment will disappear too. – Arjan Oct 21 '13 at 14:33
(And yes, my own manual "possible duplicate" comment is now deleted. But that's okay, as that was just the same as an automatic comment.) – Arjan Oct 21 '13 at 14:42
Just for the archives: a few manual comments including both "possible duplicate" and some links, were not touched today here. – Arjan Oct 30 '13 at 14:13
You're telling me even the ones without "possible" get deleted? Gah. – michaelb958 Mar 16 '14 at 10:28
I just saw a comment pointing out a duplicate on another site get deleted after a question was closed as a duplicate. That is, a comment that had the word "duplicate" and a link pointing off site. Crazy. – ff524 Feb 4 '15 at 7:15

Comments linking to duplicates which were deleted after question closure, despite having other content

Anyone else is welcome to add to the list. If you can link directly to the comment, that's best. Otherwise, link to the question.

Please note whether the comment was originally auto-generated (via a close vote) or not. (Auto-generated) (Auto-generated) (auto-generated comment which I edited was removed). Tikz: Arrow description closer to arrow (auto-generated by flagging, not close vote) This was on TeX.SE, but as I understand it, the behavior is network wide. I didn't realize that then, and asked about it on TeX meta: why was "possible duplicate" comment with additional information deleted? information-deleted

Not allowed to call release on NSString (Auto-generated)

Answering a duplicate question with a more current answer (Auto-generated)

Could someone implement a real logout? (Auto-generated)

Better way to frame "which is better" and "which is the best" type questions? (Auto-generated)

Why would you post answers to stupid questions? (Auto-generated)

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This is the opposite situation: a "possible duplicate" comment that was added by hand after having deleted the auto-generated comment. This comment is identical to the generated one, but has survived closure:

Converting string to NSDate

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Here I also added the "possible duplicate" comment myself, after I was the first to vote to close, as no comment appeared after my vote. (Maybe someone voted earlier, and retracted their close vote and deleted their automatic comment?) After the 5th close vote was cast, my manual comment was still deleted. (Which is fine in this case, but which does not match what Josh reported in this very answer.) – Arjan Oct 21 '13 at 14:44

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