Some keys dont get recognised correctly by the keylistener on some keyboard layouts.
I have found that on the german keyboard layout, the right alt key doesn't work correctly.
I haven't found keys that don't work on the US layout.

The keys dont get recognised correctly because the keylistener uses GetAsyncKeyState() to check if multiple keys are pressed at the same time., which needs virtual keycodes that are normally translated by MapVirtualKeyA(). This works most of the time but some keys are not translated correctly by MapVirtualKey() and null is returned.
Using MapVirtualKeyExA() instead of MapVirtualKeyA() did not make a difference.