`pp-eval-expression' behaves strangely under lexical binding

[Marcin Borkowski <mbork@mbork.pl>]

Hi all,

put this in an empty buffer, call `normal-mode' (so that
`lexical-binding' is set to t) and evaluate:

--8<---------------cut here---------------start------------->8---
;;; -*- lexical-binding: t; -*-
(setq spam 'eggs)
(let ((spam 'bacon))
  (pp-eval-expression 'spam)
  (message "%s" spam))
--8<---------------cut here---------------end--------------->8---

Then look at *Messages*: "eggs" is printed, then "bacon".

I wanted to use `pp-eval-expression' when debugging (basically as
a pretty-printing variant of `message'), and this behavior hit me.  Why
does this behave in this way, and is it a feature or a bug?

Best

-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University