It used to be that, when you deleted a post, the comments were also removed from the author's inbox. That was a problem if one of the comments was from a moderator to explain why the post was a removed; It simply disappeared.
So we changed that behavior.
A moderator's comments now stay in the user's inbox, even if the post is deleted. But for the comment to remain in the inbox, a few criteria have to be met:
- The comment has to be left by the moderator deleting the post.
- The comment has to be to the author of the post (not a @reply to another user).
- The post has to be deleted within one hour of leaving the comment.
How This Works
So if a user posts a question as an answer — despite all the warnings we have in place — here's how it would look:
Friendly community moderator Nick Craver sees a flag about an answer which should have been posted as another question:

He decides it's worth his time, as it's a decent question posted as an answer. So he comments on that post to educate the user:

And then immediately deletes the post:

Normally comments are deleted from the inbox when the post is deleted. But now the user will still have the moderator's message in their inbox:

When they visit the link from that inbox item, they'll see my comment and the FAQ link automatically added to their post:

That faq link on the deleted answer (this is not a new feature) points to the deletion section of the FAQ so the user can see common reasons why deletions happen:

Please note this behavior is specific to moderator comments only!