After Joomla integration upgrade to 4.3 alpha the Civicrm frontend CSS does not load anymore

Start situation: Joomla 2.5.9 and Civicrm 4.2.7. After the upgrade to Civicrm 4.3 the CSS is broken and does not seem to be loaded.
In particular the folowwing 4 files are not loaded, but possibly some of the jquery javascripts neither.
/administrator/components/com_civicrm/civicrm/css/deprecate.css
/administrator/components/com_civicrm/civicrm/css/civicrm.css
/administrator/components/com_civicrm/civicrm/css/joomla_frontend.css
/administrator/components/com_civicrm/civicrm/css/extras.css
The CSS does not seem to load in the joomla civicrm sandbox either: http://sandbox.joomla.civicrm.org/index.php?option=com_civicrm&task=civicrm/event/info&reset=1&id=3