[jQuery] What is IE7 barfing at this js?

Hi folks,

The following snippet processes a JSON string sent back to the browser (it is part of a poll)

function loadResults(data) {
  var OPT_VOTES = 2;
  var total_votes = 0;
 
  for (id in data) {
    total_votes = total_votes+parseInt(data[id][OPT_VOTES]);
                  alert("total_votes="+total_votes+" --- " + data[id][OPT_VOTES]);
  }
}

The JSON string looks like this...

[["1","High cost","23","What is the biggest challenge to recycling irrigation water?"],["2","Disease and algae management","12","5"],["3","Plentiful and cheap water","8","4"]]  

The problem I'm having is that IE7 appears to see 4 rows in the array - and consequently returns "total_votes=NaN --- undefined" at the first alert and "total_votes=NaN --- 23" at the second loop and so on.

FF, Opera, and Safari all handle the code without problem - can anyone help me understand what IE7 is getting upset about?

Thanks,

Bruce