> emacs -Q
 >
 > (setq special-display-regexps '("[ ]?[*][^*]+[*]"))
 > (setq pop-up-frame t)

I suppose you mean

(setq pop-up-frames t)

but apparently this variable is no more supported by `display-buffer'
(I'm not sure whether that's by design).

 > C-x d whatever-dir
 >
 > Mark 4 files for deletion.  Hit `x'.  Answer `yes'.
 >
 > The *Deletions* frame remains displayed.

Would the attached patch fix it?

This is NOT a generic fix - it might fail miserably if the buffer in
question is shown in two windows simultaneously.  Apparently this is no
great issue in the case at hand since `dired-pop-to-buffer' already
calls `get-buffer-window'.  I earlier provided a variable called
`display-buffer-window' for this and related issues but Stefan didn't
like it.

martin