Wicket complains about component failing to render

After upgrading wicket from version 8.10.0 to 8.11.0 my components started complain and throw exceptions about components not being rendered.

I've managed to create a quickstart with minimum steps that reproduce the bug.

The problem lies in the behavior InvisibleWhenNoChildrenVisibleBehavior which is added to ButtonPanel on line #56. This behavior worked fine until wicket 8.10.0. in wicket 8.11.0 it doesn't work anymore.