This can happen if you use Tomcat 6.0.16 or later or its plug using the same Apache EL parser as JBoss AS and WebSphere AS. You basically need to tell the Apache EL parser that it does not force primitives to their default values with the following VM argument, which is supported with Tomcat 6.0.17:
-Dorg.apache.el.parser.COERCE_TO_ZERO=false
This issue is not related to JSF. For example, this does not happen on Glassfish.
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