MetaWaylandKeyboard XKB state left stuck by IM events
It seems gnome-shell#115 (closed) unveiled some more IM fallout... A situation I very rarely saw that modifiers were left stuck in clients became very ubiquitous now (eg. after ctrl-shift-up/down). I traced this down to MetaWaylandKeyboard xkb_state being updated by events injected back by the IM.
meta_wayland_keyboard_update() should just react to real events, and no kind of generated event whatsoever.