bug#40278: 27.0.90; Flickering in Windows 10

[martin rudalics]

> Emacs frame partially covered by an Emacs frame: Nothing happens. Mouse input
> does not seem to go anywhere.

Might be that here I'm using yet another program to handle that case.
'mouse-wheel-follow-mouse' should not be involved but please make sure
that it's t.

> Emacs frame partially covered by a Windows explorer window: Emacs scrolls
> normally, that is, in my case there is some flickering. But nothing like what
> happens with a child frame.

From what Noam described the flickering could be due to the tool bar.
What happens when you write

(defun open-test ()
  (display-buffer-in-child-frame
   (get-buffer-create "test child-frame")
   '((child-frame-parameters . ((tool-bar-lines . 0)
                                (width . 20)
                                (height . 10)
                                (top . 200)
                                (left . 100))))))

instead?

martin