Homebrew will put all packages under '/usr/local/Celler' folder.
Which means if you install Git by homebrew, the installation path will look like:
/usr/local/Celler/git/1.7.8
Then homebrew will create symbol link to '/usr/local/bin' for all the binaries.

In ST system git setting window, navigate to '/usr/local/bin/git' in open file dialog, ST can find the correct path ('/usr/local/Celler/git/1.7.8'), but after upgrade Git, the path will be changed to '/usr/local/Celler/git/1.7.9'.
In this case, ST can't find the new path.
It says "System Git version launch path not accessible".

If I reopen the "Use System Git" dialog, it auto navigate to the new and real path, '/usr/local/Celler/git/1.7.9/git', not symbol link path ('/usr/local/bin/git').