frame-local variables weirdness

["Juanma Barranquero" <lekktu@gmail.com>]

After making a variable frame-local, and then buffer-local (with
`make-variable-buffer-local', not `make-local-variable') it is not
possible to set a buffer-local value for the variable:

  ELISP> (setq foo 'default)
 default
  ELISP> (make-variable-frame-local 'foo)
 foo
  ELISP> (modify-frame-parameters nil '((foo . frame)))
 nil
  ELISP> foo
 frame
  ELISP> (make-variable-buffer-local 'foo)
 foo
  ELISP> (setq foo 'bug)
 bug
  ELISP> foo
 bug
  ELISP> (frame-parameter nil 'foo)
 bug
  ELISP> (local-variable-p 'foo)
 nil

However, that doesn't happen if we first make it buffer-local, and
then frame-local:

  ELISP> (setq bar 'default)
 default
  ELISP> (make-variable-buffer-local 'bar)
 bar
  ELISP> (setq bar 'buffer)
 buffer
  ELISP> (local-variable-p 'bar)
 t
  ELISP> (make-variable-frame-local 'bar)
 bar
  ELISP> (modify-frame-parameters nil '((bar . frame)))
 nil
  ELISP> bar
 buffer
  ELISP> (kill-local-variable 'bar)
 bar
  ELISP> bar
 frame

BTW, is there a way to know when a variable is frame local?
`frame-parameter' is not enough (it could be a frame parameter and yet
not a frame local variable).

                    /L/e/k/t/u