bug#26104: 26.0.50; In Ubuntu, having mouse over other frame cause Alt key to produce a <switch-frame> event

[martin rudalics]

> switch-frame is produced when the Alt key is pressed (as soon as it is
> pressed, i.e. before the 'Y' is pressed). i can verify this by running
> 'read-event`, which triggers and produces switch-frame as soon as Alt
> is pressed. Conversely, the event is still generated even if I disable
> both my mouse and trackpad, the only things which can produce mouse
> motion.

Sorry for the silly question: Earlier you said that

  In Ubuntu, if I have two frames open and the mouse is positioned over
  the other frame (i.e. not over the active one), pressing the Alt key
  produces a <switch-frame> event.

and now you say that "the event is still generated even if I disable
both my mouse and trackpad".  How can you position the mouse when you
disable it?

martin