cannot distribute enterprise ibooks (iba)

Running Yosemite Server up to date, I am trying to distribute an enterprise books (.ibooks from iBooks Author). Profile Manager should now be able to do it as Apple claims that Yosemite server "...allows you to perform push installs of OS X enterprise apps and iOS media assets including PDF, ePub, and iBooks Author files".

But when I upload the .ibooks file into Profile Manager, the file name is changed to "shared" with a "pdf" extension and the book cannot be distributed...

Has anyone ever tried (and succeeded) to distribute an enterprise book?

Thank you!

Philippe