weird php

wut.php

<?php
$argv = array_slice( $GLOBALS['argv'], 1 );
die(var_dump(array(
    $argv,
    $argv[$i],
    serialize($argv[$i]),
    json_encode($argv[$i]),
    json_decode(json_encode($argv[$i]))
)));

/*
$i = the position of the value that starts "--require". Attained via a substr comparision in a simple FOR loop.

when above run on CLI PHP as part of a WP-CLI script, it produces (via var_dump):
*/

array(5) {
  [0] =>
  array(6) {
    [0] =>
    string(8) "@vagrant"
    [1] =>
    string(7) "--debug"
    [2] =>
    string(10) "--no-color"
    [3] =>
    string(87) "--require=src/WpcliLogger.php"
    [4] =>
    string(3) "cli"
    [5] =>
    string(7) "version"
  }
  [1] =>
  string(87) "--require=src/WpcliLogger.php"
  [2] =>
  string(95) "s:87:"--require=src/WpcliLogger.php";"
  [3] =>
  string(96) ""--require=\/Users\/paulgibbs\/Sites\/behat-vm\/behat-wordpress-extension\/src\/WpcliLogger.php""
  [4] =>
  string(87) "--require=src/WpcliLogger.php"
}

I am expecting output [1] to be the same as [3] (without the JSON formatting obviously). Note [1]'s character length given by var_dump -- 87 -- suggests the internal value is more than what's showing me. [3], the json_encoded version, shows the entire value, but even when I subsequently call json_decode, I still get back this abridged value.

I suspect it's something to do with touching $GLOBALS['argv'], which I've never really done before, but I'm pretty baffled.
This was run inside a VM running PHP 5.6.17.