there is a problem when handling wicket:fragment tags that are defined within wicket:extend tags.
the problem is in InheritedMarkupMarkupLoader:441
what happens is that first WicketTagIdentified properly assigns tag.id to be the wicket:id defined within the fragment tag
but then the InheritedMarkupMarkupLoader visits the fragment and resets its tag.id to an autogenerated id
when rendering occurs markupfragment cannot find the markup of the fragment because its tag.id has been changed