I deleted a child post of mine but I still see this message on the parent post:

"This post has child posts. Child posts are often subsequent pages of a doujinshi, or minor variations of the parent post."

Do I have to reupload the child post, add the parent post tag, remove the parent post tag, and then delete the child post again for the message to disappear altogether?

Ok well that didn't work. Got this message instead:

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That image already exists. You can find it here

An error occured. The image could not be added because it already exists or it is corrupted.
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12/30/2016 - No worries man. :)

If the message didn't go away after deleting the one and only child post, I don't know what to tell you. Sorry.