Days after the election, denounced for making the peddling of fake news remunerative, Google announced that it would no longer place ads on sites promoting clearly fabricated stories.
In fact, I think the message was once taken out of the configure script, but later restored, presumably by someone who thought it was cute and doesn't care that it's flatly incorrect.
Moving the messages will always delete their originals after the copies have been made in the destination mailbox, as implemented by mail: : IMAPClient.