After completing the demo setup, you can get a fatal error with this in the error log:
[ Aug 30 2013 12:41:55 ] [192.168.56.1] eZContentClassAttribute::eZContentClassAttribute:
Could not get instance of datatype: ezsrrating
re-posting a couple times seems to work, and data seem sane. Probably a cache issue after extensions have been enabled. Most likely related to https://jira.ez.no/browse/EZP-19411.
Code seems okay globally, but something is wrong with caching.