>> I'm not completely sure I understand the behavior you describe, but 
>> since you consider it counter-intuitive, it sounds like you might want 
>> to `M-x report-emacs-bug`.
>
> IIUC, what Zhiwei Chen described is what happens with:
>
> (define-key isearch-mode-map (kbd "M-s o") #'(lambda () (interactive) 
> (call-interactively 'isearch-occur) (pop-to-buffer "*Occur*")))
>
> Point moves to the occur buffer after you type M-s o, yet isearch has 
> not ended, so pressing "n", "p", "q", ... adds these characters to the 
> search string instead of acting in the occur buffer.
>
> I'm not sure this is a bug, but it should be possible to avoid that 
> behavior by checking e.g. in isearch-pre-command-hook that point is 
> still in the buffer in which isearch started.
>

And here is a micro-patch to fix that behavior.