Multiple Level sub-presentation unavailable in 2.1 Beta

While manipulating sub-presentations in 2.1 Beta1, it appears that sub-presentations only work up to 1 level, whereas previous versions allowed multiple layers of sub-presentation (ie : a sub-presentation inside a sub-presentation inside a sub-presentation).

While is possible within Qt 3D Studio to create a many level of depth as we want, the render doesn't display further than the 1st subpresentation