Importing xwiki-enterprise-wiki-1.3-rc-1.xar reports documents on error

Working with 1.3-RC-1.8082. While importing xwiki-enterprise-wiki-1.3-rc-1.xar in several wikis (a bunch of databases holding virtual wikis + the main database), the results show always a number of documents with errors. Like here...

Importing xwiki-enterprise-wiki-1.3-rc-1.xar: Error while importing
133 Document(s) installed
0 Document(s) skipped
4 Document(s) with error

These 4 documents are:

Main.LuceneSearch
Panels.SyntaxHelp
Photos.NewAlbum
XWiki.XWikiSyntax

The most frequent error shows just three documents failing:

Main.LuceneSearch
Panels.SyntaxHelp
Photos.NewAlbum

These are the errors logged in catalania.out...

2008-03-01 19:54:24,013
http://xpescaderias.xen.net/xwiki/bin/import/XWiki/Import?editor=import&space=XWiki
[http-80-3] ERROR packaging.Package - Failed to save document
Main.LuceneSearch
2008-03-01 19:59:32,486
http://xepecnet.xen.net/xwiki/bin/import/XWiki/Import?editor=import&space=XWiki
[http-80-7] ERROR packaging.Package - Failed to delete document
Main.LuceneSearch

The only workaround I've found is to delete the concerned documents prior to the import process. Once this has been done, any re-import works without a glitch.

Please, let me know how could I be of any further help. Thanks.