I was curious about the key, wondering if it could be hardware dependent. The semi-colon should be consistent across all hardware and OS configurations.
You've mentioned that keys are pressed in combination and held for long periods of time. The behavior of key combinations, key repeats when held down, and key repeat rates can vary widely from system to system and can usually be modified by the user. You might investigate this area and see if the settings for these things on your friend's machine are significantly different than on yours.