PHP array shows up as JSON object when encoded to JSON

This issue happens when your array indexes are not sequential.

PHP Array:

$a = array(
1 => 3,
4 => array('red'),
2 => 5
);

JSON Result:

{
  "1": 3,
  "2": 5,
  "4": [
    "red"
  ]
}

Hope it helps you out.