Unexpected behavior of Array.prototype.splice

While implementing an internal EventEmitter for a project I was working on, I came across a strange quirk when using Array.prototype.splice inside a for... in loop. The function does not successfully remove the indeces from the array within the loop:

var array = [1, 2, 3, 4, 5], index;

for (index in array) {
    if (index === 2) {
        array.splice(index, 1);
    }

    console.log(array[index]);
}

console.log(array);

Running on Google Chrome version 43, this outputs

1
2
3
4
5
[1, 2, 3, 4, 5]

when I'm expecting something like

1
2
4
5
undefined†
[1, 2, 4, 5]

Is this intential behavior or a bug? I cannot find any documented reference to this behavior.

† Possibly, if length is not calculated during each iteration of Array.prototype.splice implementation