file-precious-flag not taken seriously enough?

[Karl Fogel <kfogel@red-bean.com>]

In lisp/files.el:(basic-save-buffer-2), we have this code:

    (let ((dir (file-name-directory buffer-file-name)))
      (if (and file-precious-flag
	       (file-writable-p dir))
	  ;; If file is precious, write temp name, then rename it.
	  ;; This requires write access to the containing dir,
	  ;; which is why we don't try it if we don't have that access.
	  (let ((realname buffer-file-name)
		tempname succeed
		(umask (default-file-modes))
		(old-modtime (visited-file-modtime)))
	[...continue on to write directly to the file...]

The documentation for `file-precious-flag' doesn't say anything about
it only applying if the containing directory is writeable.  But that
seems to be how we treat it, in the conditional above.

Is this just a bug?

(Larger context: I'm implementing the `break-hardlinks-on-save' flag
as discussed in another thread, so am looking at where
`file-precious-flag' is used.)

-Karl