Hello,
The background is in https://gitlab.gnome.org/GNOME/gtk/issues/85 . One of the conclusions, in https://gitlab.gnome.org/GNOME/gtk/issues/85#note_264804 , is that mate-panel is not properly transferring focus on alt-F1 keyboard shortcut. (on alt-F2 it is working properly).
How to reproduce
install gtk3, which contains the fix for https://gitlab.gnome.org/GNOME/gtk/issues/85 (can be seen by gdk/x11/gdkdevicemanager-core-x11.c's APPEARS_FOCUSED testing for both has_focus and has_focus_window).
run the mate desktop
run accerciser, in its Event Monitor, open window element and enable window:activate and window:deactivate
run e.g. mate-terminal, accerciser shows window:activate for it
press alt-f1
Actual result
accerciser shows only window:activate for the mate-panel
Expected result
accerciser should show a window:deactivate for mate-terminal, and window:activate for mate-panel
It used to work only by luck before, only because gtk used to deactivate itself during a keyboard grab. But as discussed in https://gitlab.gnome.org/GNOME/gtk/issues/85 that behavior poses accessibility feedback issues, is not coherent, and keyboard grab feedback will not be available in wayland anyway. Thus @ebassi saying in https://gitlab.gnome.org/GNOME/gtk/issues/85#note_264804 that not transferring focus properly is the actual bug.
MATE general version
1.20
Package version
1.20
Linux Distribution
Debian