Error when searching users in the user screen in the cms configuration

Unable to search for users in the cms administration panel. When trying to search for a user an invalid query excetion error occurs.

Repoduction path:

• go in the cms to administration screen
• go to the users tab
• type a search term in the search box ('admin')
• Press 'search user'

Then the following error occurs:
21.10.2013 09:28:42 ERROR [org.hippoecm.frontend.plugins.cms.admin.SearchableDataProvider.populateList():174] Error while executing query: SELECT * FROM hipposys:user WHERE (hipposys:system <> 'true' OR hipposys:system IS NULL) AND ( fn:name() = 'mtolkamp' OR jcr:contains(hipposys:firstname, 'mtolkamp') OR jcr:contains(hipposys:lastname, 'mtolkamp') OR jcr:contains(hipposys:email, 'mtolkamp') )

javax.jcr.query.InvalidQueryException: Encountered "hipposys:firstname" at line 1, column 140.

Full stacktrace is attached.