Hello there,

I think there is a small bug with quit-window / 
quit-restore-window :

with emacs -Q

;; set some rules
(setq display-buffer-alist
      '(("\\*\\(Backtrace\\|Messages\\)\\*"
        (display-buffer-in-side-window)
        (window-height . 0.2)
        (side . bottom))))

;; trigger a logical error to display the *Backtrace* buffer
(> vim emacs)

;; display the *Messages* buffer
(view-echo-area-messages)

;; mess the `quit-restore' window parameter
(kill-buffer (get-buffer "*Backtrace*"))

;; which looks now like that in the *Messages* window :
;; ((quit-restore) (window-slot . 0) (window-side . bottom))

;; try to quit the *Messages* window
(progn (select-window (view-echo-area-messages))
       (quit-window))

;; nothing happens :

The first `cond' of quit-restore-window end up to 't,
it calls (switch-to-prev-buffer window bury-or-kill)
but there is no previous-window available.

The first patch adress this, and a similar one : when there is a previous-buffer available, but it referes to the 
same buffer. (eg: try the recipe again but exchange the role of 
*Messages* and *Backtrace*, you will finish with a blank buffer for backtrace, that you can quit again to end up to the same point)

The second patch is a proposition to clarify a little the code.