Except when I start doing anything with the keyboard. Some keys, like ESC, are merely unresponsive. Others, notably S and A, crash the game to desktop.
I went into the game menu and tried to reset my keybinds. So, for instance, I clicked on Pitch Up, which is W, and pressed the S key and the game displayed "OX91." Then I did the same for Pitch Down, which is S, and that crashed the game - instantly, with no warning and no crash dump. Using S in the gameworld - for instance, while walking - also does this. I can reliably repeat this over and over again.
I've experimented with multiple keyboards to no avail. I've tried it in windowed mode and that hasn't helped. Going into the keyboard driver area of the control panel tells me that there are no hardware conflicts, although the "update driver" button is grayed out.
Are you by chance using any special third-party keyboard driver software such as the keybind software included with the Logitech G series keyboards? If so, you may have a keybind profile loaded that is conflicting with the game. If you can't isolate the cause, you might try uninstalling or reinstalling the software to see if that fixes your issue. As long as your keyboard is USB, the generic Microsoft drivers should still allow you to use the keyboard for testing.