Previously and Initially disagree with documentation

[Patrick Stein]

From the iterate website: http://common-lisp.net/project/iterate/bugs.html
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 (iter (for el in '(1 2 3 4))
       (for p-el previous el)
       (for pp-el previous p-el initially 0)
       (collect pp-el))
gives (0 NIL 1 2); should be (0 0 1 2) according to the manual. I suspect it's a doc bug. Found by Carlos Ungil.

(iter (for el in '(1 2 3 4))
      (for pp-el previous el back 2 initially 0)
      (collect pp-el))
gives the right result.

So does:

(iter (for el in '(1 2 3 4))
      (for p-el previous el initially 0)
      (for pp-el previous p-el initially 0)
      (collect pp-el))
Without an INITIALLY 0, p-el gets set to NIL the first time through the loop. So, pp-el's value is NIL the second time through the loop. The for...previous documentation talks about the "first" and "second" value. But it doesn't detail if the initial value counts as a "first" value.
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