Import a modified zip archive fails with the GateIn Import gadget

Issue

I have deployed the gatein export / import gadged following the http://community.jboss.org/wiki/GateIn-ExportImport instructions.

While export functionality works well, when I try to import a zip file it only works if I don't make any change in the zip files.

If I unzip the generated exported file, make a minimal change in one of the files, zip again the folder (with the same zip name) and I try to import the new zip it fails,showing me the next log trace:

ERROR [gwtupload.server.UploadServlet] (ajp-0.0.0.0-8209-6) UPLOAD-SERVLET (F0F04697FB927A59336DED485FDFB52F.node1) getUploadStatus: 
     GWTMU-0852597537344371 finished with error: org.gatein.management.gadget.server.util.ProcessException: Import failed for portal container portal