I was doing some game development on a different machine than usual when I noticed that keys would occasionally stick after I released them, causing my character to keep running. At first I thought it was a bug in the new framework I was using, but I was unable to reproduce it on another machine, and I tracked the problem back to the Raw Input events that were being fired.

If I tap a key quickly, then I see the key down event fire, but the key up event isn't firing until the next time I press a key (it doesn't need to be the same key). This seems to be the case for every key on this device (E7440).

Any suggestions on how to address this? How common is this sort of low-level issue in the wild?

I have managed to reproduce it in notepad. It doesn't happen when typing (probably because notepad uses the repeat events, which do not seem to be firing?), but the problem is visible with the alt key. Key down on alt will display underlines under the shortcut keys for the menu items, and key up will then highlight the first menu item (File). When I tap quickly tap alt, the shortcut underlines are displayed, but the menu item is never highlighted.

The fact that there are no repeat events seems strange. Are those generated by Windows, or the keyboard driver?

I can't reproduce the Notepad behaviour on Win10. Maybe I'm not quick enough?

There are a whole bunch of weird keyboard behaviours due to specifications changing over the years, with certain keys being entirely virtual or sharing scancodes, but I don't recall Alt being one of them.

Having said that, you don't seem to be the first with this problem: http://stackoverflow.com/questions/2226476/problems-detecting-alt-key-on-the-control-keyup-event