Same issue here - Windows XP hotkeys worked perfectly, then after switching to Windows 7 about half of them would consistently disappear. Windows 8 does the same thing. Korean (ctrl + shift + 2) is always fine, Dvorak international (ctrl + shift + 6) always disappears.
Now that you mention it, I should share something very similar - I have also noticed that my combination LAlt+LShift+2, which is activates the Japanese IME, often keep working, but the others are lost.