On Sun, 23 Dec 2007 16:12:01 -0500 Richard Stallman <rms@gnu.org> wrote:

>     3'. Put the cursor on the first column after the left continuation arrow
>     and evaluate this sexp: (put-text-property (1- (point)) (point) 'display
>     " \n").
>
>     5. Now the rest of the text, from point to the end, appears in the same
>     position as before step 3' but the continuation arrows have vanished,
>     i.e., it looks like there are two lines of text, not one continued line.
>
> When I try this, the continuation arrows do not disappear.

This surprises me.  I continue to see what I reported with current
sources, GNU Emacs 23.0.50.2 (i686-pc-linux-gnu, GTK+ Version 2.12.0) of
2008-01-03 on escher.  Perhaps the steps I gave to reproduce it were not
clear.  I've made screen shots showing what I see.  Here is the buffer
at step 3 of my OP, before evalling the display sexp: