On X11, reactive chrome must be added to the input region in order
to work as expected. However that region works independently from
any window stacking, with the result that the unresponsive-app dialog
currently blocks all input in the "covered" area, even in windows
stacked above the unresponsive window.
The correct fix would be to track the unobscured parts of the dialog
and set the input region from that, but that's quite cumbersome. So
instead, only track chrome when the corresponding window is focused
(or the dialog itself of course).
https://gitlab.gnome.org/GNOME/gnome-shell/issues/273
b3045cb964