Normally, I can delete a comment on a post at any time after I comment.
However, if a moderator moves the post's comments to chat, I lose the ability to delete my comments that got moved to chat.
Users shouldn't be disallowed from deleting their own comments if they get moved to chat. It may not even be the user's fault, if they commented before some others started using it as extended discussions.
FYI: We had a user complain about this.