Toolbars: JCR NPE - could not reproduce

Fresh new build with prepackaged demo imported. All the site iswas published. In live mode with root, I tried to add the cache toolbar and I got (it worked next time... so perhaps linked to the prepackaged import or the first time root configures its toolbars... switching in edit mode adds correctly the toolbars and then I got no problem any more including in live mode):

2009-01-19 15:17:49,468: INFO [org.jahia.services.content.automation.RulesListener] - Executing rules for [/content/users/root/preferences/org.jahia.preferences.provider.toolbar]
2009-01-19 15:17:49,484: INFO [org.jahia.services.content.automation.RulesListener] - Rules executed for [/content/users/root/preferences/org.jahia.preferences.provider.toolbar]
2009-01-19 15:17:49,609: ERROR [org.jahia.services.preferences.impl.JahiaPreferencesJCRProvider] - Error while setting preference org.jahia.services.preferences.toolbar.ToolbarJahiaPreferenceKey@d3d872a9
javax.jcr.InvalidItemStateException: /content/users/root/preferences/org.jahia.preferences.provider.toolbar: the item cannot be saved because it has been modified externally.
at org.apache.jackrabbit.core.ItemImpl.getTransientStates(ItemImpl.java:286)
at org.apache.jackrabbit.core.ItemImpl.save(ItemImpl.java:928)
at org.jahia.services.content.JCRItemWrapperImpl.save(JCRItemWrapperImpl.java:134)
at org.jahia.services.content.JCRNodeDecorator.save(JCRNodeDecorator.java:608)
at org.jahia.services.preferences.impl.JahiaPreferencesJCRProvider.setJahiaPreference(JahiaPreferencesJCRProvider.java:718)
at org.jahia.ajax.gwt.templates.components.toolbar.server.ToolbarServiceImpl.loadGWTToolbar(ToolbarServiceImpl.java:193)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:527)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:164)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.doPost(RemoteServiceServlet.java:86)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at org.jahia.ajax.gwt.commons.server.AbstractJahiaGWTServiceImpl.service(AbstractJahiaGWTServiceImpl.java:92)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.jahia.ajax.gwt.commons.server.AbstractJahiaGWTServiceImpl.service(AbstractJahiaGWTServiceImpl.java:98)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.jahia.bin.filters.jcr.JcrSessionFilter.doFilter(JcrSessionFilter.java:56)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.tuckey.web.filters.urlrewrite.RuleChain.handleRewrite(RuleChain.java:164)
at org.tuckey.web.filters.urlrewrite.RuleChain.doRules(RuleChain.java:141)
at org.tuckey.web.filters.urlrewrite.UrlRewriter.processRequest(UrlRewriter.java:90)
at org.tuckey.web.filters.urlrewrite.UrlRewriteFilter.doFilter(UrlRewriteFilter.java:417)
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:191)
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.valves.AccessLogValve.invoke(AccessLogValve.java:568)
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:845)
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)
2009-01-19 15:17:49,640: ERROR [org.jahia.ajax.gwt.templates.components.toolbar.server.ToolbarServiceImpl] - There is no preference set for toolbar: caches
[GC 222336K->132308K(1022848K), 0.0199157 secs]
2009-01-19 15:17:54,218: INFO [org.jahia.services.search.lucene.fs.JahiaIndexSearcher] - Opening Searcher@13d09b1 main
2009-01-19 15:17:54,218: INFO [org.jahia.services.search.lucene.fs.JahiaIndexSearcher] - autowarming org.jahia.services.search.lucene.fs.JahiaIndexSearcher@13d09b1 from org.jahia.services.search.lucene.fs.JahiaIndexSearcher@188e64e
FilterCache

{cumulative_inserts=0, hits=0, cumulative_evictions=0, inserts=1, cumulative_lookups=0, lookups=0, cumulative_hitratio=0.00, cumulative_hits=0, hitratio=0.00, evictions=0, size=1}