Difference of behavior between svn 1.4.5 and 1.5.1 for svnlook diff

Hello,

here is the result of a svnlook diff command with svn 1.4.5:
   svn-1.4.5/bin/svnlook diff --revision 1607 /SVN/quattor/
   Copied: scdb/tags/2008/08/08-16.48.11 (from rev 1606, scdb/trunk)

I upgraded the server and the client to svn 1.5.1 and now the result is
empty for the same command:
   svn-1.5.1/bin/svnlook diff --revision 1607 /SVN/quattor/

Has someone an idea of the origin of this difference of result?

Thanks in advance

Best regards,
Frederic Melot