Prerequisites:
Tiling WM i3wm / xmonad -- not related to bug.
And tmux has in tmux.conf
set -g focus-events on
Test case for bug:
Open empty terminal
st -e tmux
Activate focusing
printf "\e[?1004h"
Catch one focus event
<C-v>
Move focus to another window
Expected: printed ^[[O in place of pending ^
Actual result: nothing changed
Same test case works as expected in xterm, but not in st.
Therefore I treat this misbehavior as bug.
But I haven't found any related problems inside sources.
Of course, all OK for bare st without tmux.
And we receive focus events in st+tmux when changing active pane.
But never, when we change focus of actual window.
