I think it's even worse than that. I have done exactly what Apple is asking us to do and created a book in Pages on my Mac, exporting it to ePub and dropping it into Books on my Mac. Everything shows fine in the Mac Pages file and the Mac Books ePub version.
My normal workflow is to transfer my books (in the past using Preview form IBA) to my iPad so that I can check everything works and shows as it should. Now the weird bit.
Mac /Pages file - photo galleries and videos show fine
Mac / Books ePub file - everything is present
iPad synched to transfer ePub to Books on iPad - some complete galleries, parts f galleries and videos missing
So even without the interactive content IBA allowed, not even photo galleries and 20 second video clips can be reliable displayed!