Both export and import broken

After upgrading to XWiki 1.4, I tried the export and import features : didn't work (more details below). So I tried with a clear database and the default xar package: same reaction. The war and xar files were successfully extracted by Ark (Linux archive opener), so I assume they aren't corrupted. All manipulations were made as 'superadmin'.

On Import:
The xar file upload works fine, but clicking on it won't show the pages list. After further investigations with Firebug, it seems to be a Javascript problem depending on the skin used (not 100% sure, I'm not a Javascript expert):

• Albatross: I saw several things that looks pretty much like errors in the showPackageInfos function (the file is import.js). The first one is that the object XMLHTTPRequest contains a responseXML and a responseText fields. Although responseXML is null and responseText contains what seems to be valid XML code, the responseXML field is the one used to store the XML response from the server.
  Second problem: this response is a string. The next line (84) calls the getXmlValue(tag, xml) function (line 71) whose first instruction is : var nodes = xml.getElementsByTagName(tag);
  Problem: xml is a string and therefore has no functions. As a consequence, the next thing javascript does is to throw an exception (Message: "TypeError: xml has no properties") which is catched in the respondToReadyState function (file: prototype.js).

• Toucan: I assume the showPackageInfos function is in the import.js file? According to the (HTML) source page, this file is 'skins/toucan/import.js', which is not present in the Toucan skin folder.

On export:
Weird exception (NPE maybe) occurs when clicking the 'Export' button:
Error number 11015 in 11: Exception while exporting
Wrapped Exception: null
com.xpn.xwiki.XWikiException: Error number 11015 in 11: Exception while exporting
Wrapped Exception: null
at com.xpn.xwiki.web.ExportAction.render(ExportAction.java:64)
at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:205)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.xpn.xwiki.web.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:112)
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.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:263)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:584)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:619)

Wrapped Exception:

java.lang.NullPointerException
at com.xpn.xwiki.web.ExportAction.exportXAR(ExportAction.java:228)
at com.xpn.xwiki.web.ExportAction.render(ExportAction.java:57)
at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:205)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.xpn.xwiki.web.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:112)
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.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:263)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:584)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:619)

Thanks for your help !