bug#16728: 24.3.50; bug? (with-temp-buffer (insert "foo")) deactivates mark in current buffer

[Helmut Eller <eller.helmut@gmail.com>]

On Fri, Feb 14 2014, Stefan Monnier wrote:

>>  (list (with-temp-buffer
>>         (set (make-local-variable 'deactivate-mark) nil)
>>         (insert "foo")
>>           (let (deactivate-mark)
>>             (with-temp-buffer
>>               (insert "bar"))))
>>        deactivate-mark)
>
> The `let' above dynamically binds the `deactivate-mark' of the first
> temp-buffer.  The (insert "bar") then set the deactivate-mark in the
> second temp-buffer, which did not make it buffer-local, so it really
> sets the global deactivate-mark.  Try:
>
>    (with-temp-buffer
>      (let ((a 3)
>            (buf (current-buffer)))
>        (make-local-variable 'a)
>        (let ((a 4))
>          (with-temp-buffer
>            (message "a=%S but a=%S" (list a (local-variable-p 'a))
>                                     (with-current-buffer buf
>                                       (list a (local-variable-p 'a))))))))
>
> Interaction between let-bindings and buffer-local bindings is tricky.

This prints "a=(3 nil) but a=(4 t)". "a=(4 nil) but a=(3 t)" would be
less surprising.

Why is it this way?  This behavior of let seems non-intuitive and
rather useless to me.  I don't suppose that there is a variant of let
that does what I want?

Helmut