Hi Juri,

>> There are a couple of ways to improve behavior of perform-replace:
>>
>> - Use a different name for the query-replace help buffer (patch attached)
>> - Make 'C-l' or some other key bury the help buffer, if it was displayed
>>   in the main window
>> - Make '?' toggle visibility of the help buffer
>> - Allow switching windows in query-replace
>> - Display the help message in the minibuffer
>
> To solve the same problem, isearch binds display-buffer-overriding-action
> to isearch--display-help-action with '(nil (inhibit-same-window . t))
> that forces the *Help* buffer to be displayed in another window.

Thanks for letting me know.  I'm attaching a different patch which uses
display-buffer-overriding-action.  Does it look OK?