I don't think this is portlet-specific, but the only way I could reproduce it quickly was to introduce the problem into a portlet I was working with.

The attached portlet uses just-ice.jar instead of icefaces.jar

In addition, the JobApplication.jspx page contains the following HTML fragment;
        <p>hello</p>

And when the portlet is loaded on the page, the portlet is not displayed, and the following stacktrace appears in the console log:

18:07:23,040 ERROR [Parser:139] Failed to execute JSP lifecycle.
java.lang.NullPointerException
        at javax.faces.component.UIComponentBase.encodeBegin(UIComponentBase.java:703)
        at javax.faces.webapp.UIComponentTag.encodeBegin(UIComponentTag.java:613)
        at javax.faces.webapp.UIComponentTag.doStartTag(UIComponentTag.java:500)
        at com.icesoft.faces.webapp.parser.Parser.executeJspLifecycle(Parser.java:162)

Recommend that the a Log4J warning be logged instead, and that any markup other than <ice: and <f: simply be ignored by the parser.