The docopt documentation suggests that a lone "--", signifying the end of the command-line flags, is only supported if "[--]" is added explicitly to the syntax string. In my opinion this is a mistake, and may even break POSIX XBD §12 [1]. I would seriously recommend the authors support it by default.
[1]: http://pubs.opengroup.org/onlinepubs/009604499/basedefs/xbd_...