Reported here: http://blog.sourcetreeapp.com/2013/12/11/sourcetree-for-mac-1-8-subtree-support-mavericks-improvements/#comment-1221106811

Issue described here: http://stackoverflow.com/questions/19712735/git-svn-cannot-setup-tracking-information-starting-point-is-not-a-branch

Critical as you can't checkout branches for tracking in git-svn