Problem with duplicate text content after change of publication date

I have encountered this problem that duplicates the content of the post.
My client writes the content of the post then does not make it public, when she decides to post the post then falls back and changes the post creation and posting dates and save, at this point the content of the post is duplicated.

For example, if in the post I write:
sample text
and then I go back to the dates and save me he writes to me
sample text
readmore
sample text


thanks a lot

stefano