#423 is intended to avoid keys being "stuck down" due to the release event not being delivered when the focus is changed with the key pressed. This handles some cases, but not all.

rust-windowing added the concept of synthetic events to address the same issue, see:

• Tracking Issue: Sync key press/release with window focus rust-windowing/winit#1272
• X11: Sync key press/release with window focus rust-windowing/winit#1296

However there are cases where a synthetic key Pressed event is delivered, but a corresponding Release event isn't. This can be reliably reproduced on Ubuntu 20.04 by changing workspaces (Ctrl-Alt-Up/Down Arrow) while Gt has window focus.