> This patch produces the desired behavior for me and matches
 > the xemacs behavior when I use the following.
 >
 > (setq display-buffer-base-action '((display-buffer-use-least-recent-window)
 > (not-this-window . t)))
 >
 > The explicit not-this-window is required to get display-buffer-pop-up-window
 > to trigger in a single window single frame case. It might be worth adding a
 > note
 > to that effect to the docstring?

Silly me.  Please try again with the attached.  Then

(setq display-buffer-base-action '((display-buffer-use-least-recent-window)))
(display-buffer "*Messages*")

should work as expected.

 > This results in the behavior of the example matching that of xemacs.
 > With the lru-time option enabled the display multiple buffers case seems
 > to be served (I assume there is some other mechanism that can be used
 > to restore the previous window configuration in such cases that is not
 > included in this example).

Sorry.  I don't grok what you said in parentheses here.

martin