I did a clean checkout of a repository then every day I have an hudson job that runs a script to backup the configuration. Part of the script is to add *.xml
Seems like the correct behaviour for SVN 1.7. An alternative is to add only unversioned files:
svn st *.xml | grep ? | tr -s ' ' | cut -d ' ' -f 2 | xargs svn add
However it's possible you have nothing to add, so you will get
svn: E205001: Try 'svn help' for more info
svn: E205001: Not enough arguments provided
Related question: Add all unversioned files to Subversion using one Linux command