I've not been able to recreate this error - it obviously depends very much on the multipart form data!
But it definitely looks like a bug.

java.lang.ArrayIndexOutOfBoundsException: 2048
 at org.jboss.seam.web.MultipartRequest.checkSequence(MultipartRequest.java:466)
 at org.jboss.seam.web.MultipartRequest.parseRequest(MultipartRequest.java:333)
 at org.jboss.seam.web.MultipartRequest.getParam(MultipartRequest.java:507)
 at org.jboss.seam.web.MultipartRequest.getParameter(MultipartRequest.java:558)
 at org.apache.myfaces.context.servlet.RequestParameterMap.getAttribute(RequestParameterMap.java:39)
 at org.apache.myfaces.context.servlet.AbstractAttributeMap.get(AbstractAttributeMap.java:87)
 at com.sun.facelets.tag.ui.UIDebug.debugRequest(UIDebug.java:119)
 at com.sun.facelets.FaceletViewHandler.restoreView(FaceletViewHandler.java:305)
 at org.ajax4jsf.framework.ViewHandlerWrapper.restoreView(ViewHandlerWrapper.java:116)
 at org.ajax4jsf.framework.ajax.AjaxViewHandler.restoreView(AjaxViewHandler.java:147)
 at org.apache.myfaces.lifecycle.LifecycleImpl.restoreView(LifecycleImpl.java:141)
 at org.apache.myfaces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:66)
 at javax.faces.webapp.FacesServlet.service(FacesServlet.java:137)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
 at org.jboss.seam.web.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:63)
 at org.jboss.seam.web.RedirectFilter.doFilter(RedirectFilter.java:45)
 at org.jboss.seam.web.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:49)
 at org.jboss.seam.web.ExceptionFilter.doFilter(ExceptionFilter.java:57)
 at org.jboss.seam.web.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:49)
 at org.jboss.seam.web.MultipartFilter.doFilter(MultipartFilter.java:74)
 at org.jboss.seam.web.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:49)
 at org.jboss.seam.web.SeamFilter.doFilter(SeamFilter.java:84)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
 at org.ajax4jsf.framework.ajax.xmlfilter.BaseXMLFilter.doXmlFilter(BaseXMLFilter.java:96)
 at org.ajax4jsf.framework.ajax.xmlfilter.BaseFilter.doFilter(BaseFilter.java:220)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
 at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
 at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
 at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
 at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:175)
 at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:432)
 at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:74)
 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
 at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
 at org.jboss.web.tomcat.tc5.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:156)
 at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
 at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
 at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:199)
 at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:282)
 at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:767)
 at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:697)
 at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:889)
 at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
 at java.lang.Thread.run(Thread.java:595)