Overridden API method of a JSF component is not getting called.

I have a Richfaces component, that extends the javax.faces UISelectMany, and overrides the method "validateValue".
in AS 7, my overridden method does not get called, but it does get called in AS 6.
I've looked at the AS7 mojarra source:
https://github.com/jboss/mojarra/blob/2.0.4-b09-jbossorg/jsf-api/src/main/java/javax/faces/component/UISelectMany.java#L580
And the method I'm overriding is indeed present.

Any idea what could be causing this problem? A modules/classpath visibility problem perhaps?