At some point all files in my working copy got marked with \"S\" symbol as shown below:
$ svn st
M S AclController.php
S InstallationController.php
In case anyone is coming in late looking for the answer (which is stated correctly above), I believe a likely CAUSE of this situation is an 'svn switch' on a parent directory that fails (as in the case of a local uncommitted file with the same name, and no --force option), leaving all files subsequent to the failure 'un-switched'.
That is why (assuming the original issue is later corrected) a subsequent 'svn switch' again on the same parent directory will indeed switch the remaining un-switched files to a new repo path.