The latest xcode (4.6) ships with an older SVN (1.6) and so does osx!
State of the art (as far that can be set for SVN :D) is 1.7

now, when you use some third party tools like Cornerstone SVN they might default to 1.7

1.7 working copies cannot be read/modified with 1.6 and so Xcode will fail to read the history for such working copies.

To upgrade XCode (and if you like, the osx default client):

1. download svn

   cd ~/Downloads/
   curl -o subversion-latest.tar.gz http://apache.mirrors.tds.net/subversion/subversion-1.7.8.tar.gz
   tar -xvf subversion-latest.tar.gz

2. build & install svn (with neon support! for http/https)

   cd ~/Downloads/subversion-1.7.*
   sh get-deps.sh neon
   cd neon/
   ./configure --with-ssl
   make
   sudo make install
   cd ..
   ./configure --prefix=/usr --with-neon
   make
   sudo make install

IF YOU don't want to install it as system default, choose another prefix.. e.g.: ./configure --prefix=/usr/local --with-neon

1. go into the Xcode bundle and tell it to use the new binaries

   cd /Applications/Xcode.app/Contents/Developer/usr/bin/
   sudo -s
   ln -s /usr/bin/svn* ./

IF YOU didn't install it as system default, the path is different depending on the prefix you chose