In Firebug, we can see the sorting causes a POST, and this is the response. Evidently, JSF has encountered an error, and then has had an error while trying to report the first one.
<html><head><title>Apache Tomcat/7.0.20 - Error report</title><style><!--H1
{font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:22px;}
H2
{font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:16px;}
H3
{font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:14px;}
BODY
{font-family:Tahoma,Arial,sans-serif;color:black;background-color:white;}
B
{font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;}
P
{font-family:Tahoma,Arial,sans-serif;background:white;color:black;font-size:12px;}
A
{color : black;}
A.name
{color : black;}
HR
{color : #525D76;}
--></style> </head><body><h1>HTTP Status 500 - </h1><HR size="1" noshade="noshade"><p><b>type</b> Exception report</p><p><b>message</b> <u></u></p><p><b>description</b> <u>The server encountered an internal error () that prevented it from fulfilling this request.</u></p><p><b>exception</b> <pre>java.lang.IllegalStateException: CDATA tags may not nest
com.sun.faces.renderkit.html_basic.HtmlResponseWriter.startCDATA(HtmlResponseWriter.java:630)
javax.faces.context.ResponseWriterWrapper.startCDATA(ResponseWriterWrapper.java:172)
javax.faces.context.PartialResponseWriter.startError(PartialResponseWriter.java:342)
org.icefaces.ace.context.CallbackPartialResponseWriter.startError(CallbackPartialResponseWriter.java:120)
com.sun.faces.context.AjaxExceptionHandlerImpl.handlePartialResponseError(AjaxExceptionHandlerImpl.java:200)
com.sun.faces.context.AjaxExceptionHandlerImpl.handle(AjaxExceptionHandlerImpl.java:123)
org.icefaces.impl.application.ExtendedExceptionHandler.handle(ExtendedExceptionHandler.java:109)
com.sun.faces.lifecycle.Phase.doPhase(Phase.java:119)
com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
javax.faces.webapp.FacesServlet.service(FacesServlet.java:594)
</pre></p><p><b>note</b> <u>The full stack trace of the root cause is available in the Apache Tomcat/7.0.20 logs.</u></p><HR size="1" noshade="noshade"><h3>Apache Tomcat/7.0.20</h3></body></html>
I wouldn't have thought this would work in the first place. Sorting + grouped headers was a incompatibility captured in
ICE-7028.