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How did you know that someone gave you a 1? Can you see a list of the value of every vote somewhere? If so, you'll note that you just got another 10! 
Joe >>
It's easy to tell if you closely monitor your User Rating all the time (why you'd do that is kinda odd, but anyway).
For instance, danzig now has:
User Rating: 6.91
No of votes: 38
If his rating suddenly dropped down to 6.76, which is [(6.91*38+1)/39], with one more vote, then he knows that added vote was a '1'.
To address your original question
danzig, some users might give you a 1 because they inadvertently believe that '1' is the highest rating instead of the lowest. I've seen several threads asking just that.