Regression: async components are not rendered anymore

Async components are not rendered anymore. The Ajax calls that fetch the components and replace them in the page don't seem to happen anymore.

Steps to reproduce:
1. start the Essentials archetype with the 'news' feature added
2. make the top menu asynchronous: open http://localhost:8080/cms/console/?path=/hst:hst/hst:configurations/myhippoproject/hst:abstractpages/base/menu and add the property 'hst:async' with value 'true'
3. open http://localhost/site

Expected: the home page is rendered including the top menu
Actual: the top menu is no longer visible