On 24.2, describe-variable shows the name of the current buffer, even if passed a different buffer.
Apply the attached descfunorvar.patch (see my post to emacs-devel, "Unify fn and var help to make learning elisp a little easier" for details) to 24.2. Then do emacs -Q, then
C-SPC C-h o mark-active RET

It says, "Its value is t
Local in buffer *Help*"

It should say, "Its value is t
Local in buffer *scratch*"

The attached helpfnsbug.patch fixes the bug.