The page size in now hidden on the rendition tab and per default filled in with an incorrect value. Make the property (also?) visible on the details place leave it empty and required when there is no good way to set the defaults. Now renditions are created that are not useable (A4 document on A0 landscape).
Page Size is part of the Rendition Properties, which is a mandatory page. Added Page Size to the Details page would clutter the page more