Iframe in scheduled post disappear when publishing

Hi, I had a few post that embedded, via iframe YouTube videos or Scribd document, and i scheduled them for later publishing.

While the post were in draft, the embedded content was just fine, but when the post was published the iframe disappeared. If I re-insert it again, it then works fine again.

I was wandering what could cause the loss of the iframe when post status changed from draft to published.

Thank you,
Marco