Direct assignment is ignored when followed by creating a new observer

[mennovanslooten]

var a = ['bar'];

_.observe(a, 'update', function(new_item, old_item, item_index) {
    console.log(new_item + ' was changed from ' + old_item + ' at ' + item_index);
});

// should log "foo was changed from bar at 0"
a[0] = 'foo';

// Prevents 'foo' from being picked up
_.observe(a, 'delete', function() { });