bug#34770: <scroll> is undefined

[Eli Zaretskii]

> From: Mikhail <mike.merinov@gmail.com>
> Date: Wed, 6 Mar 2019 17:19:28 +0300
> 
> When I switch to it from WSL window or Cisco Jabber, but not from
> Firefox, some scroll event is sent to emacs window, which occurs in
> messages every second or so:
> <scroll> is undefined [4 times]
> and breaks every hotkey (C-x, C-c, or spacemacs Space-<something>).

This means that somehow Emacs receives the Scroll Lock key (that is
what produces the <scroll> "function key" event).

> Here is more details:
> https://github.com/syl20bnr/spacemacs/issues/12021
> 
> This seems buggy to me.

I see no bug here: something sends the Scroll Lock keypress to Emacs,
and Emacs reacts as expected.

I suggest to find out which part of Windows or some other software
sends that keypress to Emacs and disable that.  Failing that, you
could try working around the problem by setting
w32-scroll-lock-modifier to the value t.