The documentation states that only the lo-order bit is reliable : https://docs.microsoft.com/en-us/windows/desktop/api/winuser/nf-winuser-getasynckeystate

but https://cs.chromium.org/chromium/src/ui/events/blink/web_input_event_builders_win.cc?q=GetAsyncKeyState&sq=package:chromium&dr=C

uses 0x8000 as a mask (extracting the hi-order bit).