declared error-page not called for a JasperException

I've a general error-page which handles all types of Exceptions (e.g. JasperException -> shows een the line with the error)

• I declare an error-page in web.xml like this

  	<error-page>
  		<exception-type>org.apache.jasper.JasperException</exception-type>
  		<location>/error-page.jsp</location>
  	</error-page>
  

This page is never called on an exception org.apache.jasper.JasperException: /WEB-INF/classes/de/dwpbank/wpdirect/vienna/ug0001samples/uc0004layout/pages/layout1.jsp(13,6) No such tag ro in the tag library imported with prefix v

Reason:

• The Throwable above will be set to Dispatcher.ForwardAttributes by the key javax.servlet.error.exception but this method suppresses all keys starting on "javax.servlet", so the ErrorPageErrorHandler can never forward to it !

Why does the Dispatcher.ForwardAttributes.setAttribute(...) does that ?