> The code imposes this as one of the conditions for fitting the window
 > to the buffer:
 >
 > (or (not (frame-parameter frame 'minibuffer))
 >     (let ((mini-window (minibuffer-window frame)))
 >       (or (null mini-window)
 >           (not (eq frame (window-frame mini-window)))
 >                (< (nth 3 edges) (nth 1 (window-edges mini-window)))
 >                (> (nth 1 edges) (frame-parameter frame 'menu-bar-lines)))))
 >
 > I don't understand the last condition (>). At the least, this
 > condition seems to be missing from the doc string:
 >
 > "Do nothing if the buffer contains more lines than the present window
 > height, or if some of the window's contents are scrolled out of view,
 > or if shrinking this window would also shrink another window, or if
 > the window is the only window of its frame."
 >
 > What is that last condition (>) for?  What is the relation between the
 > number of menu-bar-lines and the `Top' position of the window?

I guess it's a poor man's attempt to make sure that there's some other
window above or below the one to shrink.

 > And doesn't this code raise an error if the `menu-bar-lines' parameter
 > is nil? Should it really be doing that?

Looks like a bug.  Could you try the attached patch?  Since this code
hasn't been touched for quite some time we can't fix it for Emacs 23.1
though.

martin