Hi all!
We have a webapp running with Seam/RichFaces in production. Running a performance test with JUnitPerf and HtmlUnit we just found out that if we access the webapp with multiple threads right after it has been started we get this fatal linkage error:

2010-08-13 11:03:26,605 INFO  - facelets.compiler: Added Library from: jar:file:/c:/.m2/repository/com/sun/facelets/jsf-facelets/1.1.14/jsf-facelets-1.1.14.jar!/META-INF/jsf-core.taglib.xml
2010-08-13 11:03:26,605 INFO  - facelets.compiler: Added Library from: jar:file:/c:/.m2/repository/com/sun/facelets/jsf-facelets/1.1.14/jsf-facelets-1.1.14.jar!/META-INF/jsf-html.taglib.xml
2010-08-13 11:03:26,621 INFO  - facelets.compiler: Added Library from: jar:file:/c:/.m2/repository/com/sun/facelets/jsf-facelets/1.1.14/jsf-facelets-1.1.14.jar!/META-INF/jsf-ui.taglib.xml
2010-08-13 11:03:26,637 INFO  - facelets.compiler: Added Library from: jar:file:/c:/.m2/repository/com/sun/facelets/jsf-facelets/1.1.14/jsf-facelets-1.1.14.jar!/META-INF/jstl-core.taglib.xml
2010-08-13 11:03:26,637 INFO  - facelets.compiler: Added Library from: jar:file:/c:/.m2/repository/com/sun/facelets/jsf-facelets/1.1.14/jsf-facelets-1.1.14.jar!/META-INF/jstl-fn.taglib.xml
2010-08-13 11:03:26,652 INFO  - facelets.compiler: Added Library from: jar:file:/c:/.m2/repository/org/jboss/seam/jboss-seam-ui/2.1.2/jboss-seam-ui-2.1.2.jar!/META-INF/s.taglib.xml
2010-08-13 11:03:26,652 INFO  - facelets.compiler: Added Library from: jar:file:/c:/.m2/repository/org/jboss/seam/jboss-seam-pdf/2.1.2/jboss-seam-pdf-2.1.2.jar!/META-INF/seam-pdf.taglib.xml
2010-08-13 11:03:26,668 INFO  - facelets.compiler: Added Library from: jar:file:/c:/.m2/repository/org/jboss/seam/jboss-seam-excel/2.1.2/jboss-seam-excel-2.1.2.jar!/META-INF/seam-excel.taglib.xml
2010-08-13 11:03:26,683 INFO  - facelets.compiler: Added Library from: jar:file:/c:/.m2/repository/org/jboss/richfaces/richfaces-ui/3.3.0.GA/richfaces-ui-3.3.0.GA.jar!/META-INF/a4j.taglib.xml
2010-08-13 11:03:26,683 INFO  - facelets.compiler: Added Library from: jar:file:/c:/.m2/repository/org/jboss/richfaces/richfaces-ui/3.3.0.GA/richfaces-ui-3.3.0.GA.jar!/META-INF/ajax4jsf.taglib.xml
2010-08-13 11:03:26,683 INFO  - facelets.compiler: Added Library from: jar:file:/c:/.m2/repository/org/jboss/richfaces/richfaces-ui/3.3.0.GA/richfaces-ui-3.3.0.GA.jar!/META-INF/jsp.taglib.xml
2010-08-13 11:03:26,746 INFO  - facelets.compiler: Added Library from: jar:file:/c:/.m2/repository/org/jboss/richfaces/richfaces-ui/3.3.0.GA/richfaces-ui-3.3.0.GA.jar!/META-INF/rich.taglib.xml
2010-08-13 11:03:26,746 INFO  - facelets.compiler: Added Library from: jar:file:/c:/.m2/repository/org/jboss/richfaces/richfaces-ui/3.3.0.GA/richfaces-ui-3.3.0.GA.jar!/META-INF/richfaces.taglib.xml
2010-08-13 11:03:28,119 ERROR - ch.rtc.cyberibis.admin.components.ExceptionsHandler: javax.servlet.ServletException: Servlet execution threw an exception
2010-08-13 11:03:28,119 ERROR - ch.rtc.cyberibis.admin.components.ExceptionsHandler: org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:313)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
ch.rtc.cyberibis.admin.web.servlet.filter.TimingFilter.doFilter(TimingFilter.java:44)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:83)
org.jboss.seam.web.IdentityFilter.doFilter(IdentityFilter.java:40)
org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
org.jboss.seam.web.MultipartFilter.doFilter(MultipartFilter.java:90)
org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
org.jboss.seam.web.ExceptionFilter.doFilter(ExceptionFilter.java:64)
org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
org.ajax4jsf.webapp.BaseXMLFilter.doXmlFilter(BaseXMLFilter.java:178)
org.ajax4jsf.webapp.BaseFilter.handleRequest(BaseFilter.java:290)
org.ajax4jsf.webapp.BaseFilter.processUploadsAndHandleRequest(BaseFilter.java:390)
org.ajax4jsf.webapp.BaseFilter.doFilter(BaseFilter.java:517)
org.jboss.seam.web.Ajax4jsfFilter.doFilter(Ajax4jsfFilter.java:56)
org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
org.jboss.seam.web.LoggingFilter.doFilter(LoggingFilter.java:60)
org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
org.jboss.seam.servlet.SeamFilter.doFilter(SeamFilter.java:158)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:433)
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
java.lang.Thread.run(Thread.java:619)

2010-08-13 11:03:28,244 ERROR - org.jboss.seam.exception.Exceptions: handled and logged exception
javax.servlet.ServletException: Servlet execution threw an exception
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:313)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at ch.rtc.cyberibis.admin.web.servlet.filter.TimingFilter.doFilter(TimingFilter.java:44)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:83)
    at org.jboss.seam.web.IdentityFilter.doFilter(IdentityFilter.java:40)
    at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
    at org.jboss.seam.web.MultipartFilter.doFilter(MultipartFilter.java:90)
    at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
    at org.jboss.seam.web.ExceptionFilter.doFilter(ExceptionFilter.java:64)
    at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
    at org.ajax4jsf.webapp.BaseXMLFilter.doXmlFilter(BaseXMLFilter.java:178)
    at org.ajax4jsf.webapp.BaseFilter.handleRequest(BaseFilter.java:290)
    at org.ajax4jsf.webapp.BaseFilter.processUploadsAndHandleRequest(BaseFilter.java:390)
    at org.ajax4jsf.webapp.BaseFilter.doFilter(BaseFilter.java:517)
    at org.jboss.seam.web.Ajax4jsfFilter.doFilter(Ajax4jsfFilter.java:56)
    at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
    at org.jboss.seam.web.LoggingFilter.doFilter(LoggingFilter.java:60)
    at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
    at org.jboss.seam.servlet.SeamFilter.doFilter(SeamFilter.java:158)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:433)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
    at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.LinkageError: loader (instance of  org/apache/catalina/loader/WebappClassLoader): attempted  duplicate class definition for name: "org/ajax4jsf/component/RenderPhaseUIDataAdaptorVisitor"
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:621)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
    at java.net.URLClassLoader.access$000(URLClassLoader.java:56)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
    at org.apache.catalina.loader.WebappClassLoader.findClass(WebappClassLoader.java:887)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1327)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1206)
    at org.ajax4jsf.util.ServicesUtils.loadClass(ServicesUtils.java:143)
    at org.richfaces.util.RenderPhaseComponentVisitorUtils.init(RenderPhaseComponentVisitorUtils.java:76)
    at org.richfaces.util.RenderPhaseComponentVisitorUtils.getVisitors(RenderPhaseComponentVisitorUtils.java:55)
    at org.richfaces.event.RenderPhaseComponentListener.beforePhase(RenderPhaseComponentListener.java:64)
    at org.ajax4jsf.component.AjaxViewRoot.processPhaseListeners(AjaxViewRoot.java:185)
    at org.ajax4jsf.component.AjaxViewRoot.encodeBegin(AjaxViewRoot.java:502)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:884)
    at com.sun.facelets.FaceletViewHandler.renderView(FaceletViewHandler.java:592)
    at org.ajax4jsf.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:100)
    at org.ajax4jsf.application.AjaxViewHandler.renderView(AjaxViewHandler.java:176)
    at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:106)
    at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:251)
    at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:144)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:245)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    ... 33 more

On the other hand if we access the webapp with a single thread after startup and then run our performance test, all goes well.

Any ideas?