On which OS version? And what file-system format is the destination disk?
Whatever OS version or file-system I try that on, it sees "." as an existing directory. That makes it fall into the pattern "ln -s source_file target_dir", which creates the file "./leafname", where "leafname" is the final pathname component of source_file. See the 'ln' man page for details.
If there is some directory that doesn't have an entry named ".", then that directory is damaged. Also, the "." entry should always refer to the enclosing directory itself. The fact that this happened at all suggests you may have some latent file-system damage. Consider running "Verify Disk" in Disk Utility.app, and see if any errors are listed.