frame-local variables weirdness

[Juanma Barranquero]

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