This bug only occurs on a Windows laptop with a built in IR receiver that automatically installs a driver for "Microsoft eHome MCIR 109 Keyboard" even though no such keyboard comes with it, or has ever been used with it. This bug effects all programs using DirectInput to read keyboard scancodes, unless they are aware of it. Any keyboard used with such a PC, even the built-in laptop keyboard, will generate incorrect scancodes with DirectInput. But RawInput and Virtual Key codes will be correct.

This bug is documented in the DOSBox Manual, as it has a major effect on DOSBox since users can't change directories:
"KEYBOARD: Right Shift and "\" doesn't work in DOSBox. (Windows only)
This may happen if Windows thinks that you have more than one keyboard connected to your PC when you use some remote control devices. To verity this problem run cmd.exe, navigate to DOSBox program folder and type:
set sdl_videodriver=windib
dosbox.exe
check whether keyboard started to work properly. As windib is slower it is best to use one of the two solutions provided here: http://vogons.zetafleet.com/viewtopic.php?t=24072"

The bug can be detected like this (pascal):

    KeyboardDevice.SetDataFormat(c_dfDIKeyboard);
    KeyboardDevice.Acquire;
    // Check for Japanese Scan code bug
    didw.diph.dwSize:=sizeof(didw);
    didw.diph.dwHeaderSize:=sizeof(DIPROPHEADER);
    didw.diph.dwHow:=DIPH_BYOFFSET;
    didw.diph.dwObj:=$94;
    JapaneseScancodeBug:=Succeeded(KeyboardDevice.GetProperty(DIPROP_SCANCODE, didw.diph)) and (didw.dwData=$29);

This code gets the scancode for scancode $94, and if it succeeds and says the scancode for scancode $94 is $29 (`~), then the bug is present. (It should fail or return $14E0).

The bug can be fixed like this (pascal):

// This is the "DOSBox/SDL/DirectInput" bug caused by laptops with an IR sensor
// automatically installing keyboard device "Microsoft eHome MCIR 109 Keyboard"
function FixJapaneseScancode(badsc: Word): Word;
begin
  case badsc of
    $1A: Result:=$1B;
    $1B: Result:=$2B;
    $2B: Result:=$55;
    $90: Result:=$0D;
    $91: Result:=$1A;
    $92: Result:=$28;
    $94: Result:=$29;
    else Result:=badsc;
  end;
end;

If JapaneseScancodeBug is true, you should call this function for every scancode to get the real scancode.

I call it the JapaneseScancodeBug because 109 key keyboards, like the one it thinks is installed, are Japanese. The bug probably occurs with real Japanese keyboards too.