why does community user delete answers on close of question?

Question

As part of Project Management SE's cleanup efforts, I closed a question as not constructive. Afterwards, I went to leave a comment explaining why and noticed the post was locked by the Community user. Additionally, 3 of the answers on the post were also marked as both locked and deleted by the Community user.

The posts were marked locked and deleted at the same time as when I closed the question. Here is a link to the question: https://pm.stackexchange.com/questions/2549/points-to-nail-down-when-agreeing-to-develop-software-on-spec

For those who aren't 2k users on the site, here is a screenshot:

Note that the locked and deleted times both say "37 minutes ago" At the time of this writing, it's been exactly 37 minutes since I closed this post.

Why did the Community user delete these answers and lock the post? There doesn't seem to be a pattern I can see. Two answers are from users without an account, due to migration, but the last answer belongs to an active user. Other answers were not deleted.

I did not observe if the answers were deleted prior to closing the post, but the fact that they were marked as deleted at the same time suggests they were not in fact previously deleted.

Out of curiosity, I reopened the question to see if the answers would be undeleted. They were still marked deleted. I also tried to check the post history but couldn't find any helpful information.

My motivation for asking is to gain a better understanding of how the system works. If this post were to be flagged to be reopened, should those answers also be undeleted? I ask because I'm not sure if they were originally self-deleted or moderator deleted and then the Community user decided to take ownership, or if there is something else going on that I don't understand or am not aware of.

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UPDATE: With @animuson's help, we determined the migrated answers posted originally on the source site are deleted while answers posted on the target site remain.

With that said, the list of answers actually support my justification for closing the questions as a list/poll, yet only 2k+ users will see this.

Why does this happen? Is it inappropriate to undelete them?

Answer 1

As you've found, this occurs when you close (for any reason other than Exact Duplicate or "Belongs on ....") a question that has been migrated to your site.

Why? Because otherwise you can end up with the rather problematic situation of having the same answers by the same users on multiple sites, both sets of them on closed questions. If the question is worth salvaging, that should be done on one site; chances are, answerers aren't going to invest time in updating their answers in two places. So the rejected question is locked, and the answers are locked and deleted, to send the message that it once again belongs to the originating site.

If you want the question, don't close it. If you have to close it without rejecting the migration, clear the migration history first (this option exists in the mod menu). Otherwise, please leave the answers deleted and the question locked after the migration has been rejected.

Answer 2

It's a sort of awkward artifact of migration rejection; it's supposed to kick all (migrated) answers back to the original site, where they'll be undeleted.

If you want to keep all answers on your site, clear the migration history and the post should be unlocked/answers undeleted and the post will act like any other closed post on your site.

As a side note, weirdness like this is why I usually just delete migrated questions to reject them; it's much cleaner. If it's close-worthy but you find it valuable to keep around for some reason, don't delete but instead clear the migration history and close. I don't have as much experience with the later option though.