I've already seen this issue on a couple of machines and on the web (see for instance http://help.lockergnome.com/office/Triple-letters--ftopict1004117.html).
At random, Word 2010 (in my case) triples the character that should appear as single and I press something like Left, Home, Backspace or Page Up, it becomes unresponsive and I lose my work. However small amount is lost, the unpredictability of the issue is annoying.
I don't think keyboard physical state could be the reason, because I've only seen this behavior in Word and no other programs behave this way.
Any ideas how to troubleshoot?