set-window-start in Elisp manual

[Stephen Berman]

Node Window Start of the Emacs Lisp manual give the following example of
using set-window-start:

          ;; Here is what `foo' looks like before executing
          ;;   the `set-window-start' expression.

          ---------- Buffer: foo ----------
          -!-This is the contents of buffer foo.
          2
          3
          4
          5
          6
          ---------- Buffer: foo ----------

          (set-window-start
           (selected-window)
           (1+ (window-start)))
          => 2

          ;; Here is what `foo' looks like after executing
          ;;   the `set-window-start' expression.
          ---------- Buffer: foo ----------
          his is the contents of buffer foo.
          2
          3
          -!-4
          5
          6
          ---------- Buffer: foo ----------

When I try this (in GNU Emacs 23.0.50.2 (i686-pc-linux-gnu, GTK+ Version
2.12.0) of 2008-01-16 on escher, also with -Q), the sexp does eval to 2,
but window-start and point remain at 1, and the buffer display does not
change.  Is the example wrong, or is there a bug in set-window-start, or
am I misunderstanding the example?  (If the latter, then I also do not
understand how set-window-start is supposed to work, so in that case I
would appreciate clarification.)

Steve Berman