Description:
------------
When the same variable is 'used' by one closure by reference an another closure 'uses' the same variable by value, both behave like were 'using' the var by value. I think the demonstration code will help making things clear for you.
Not less stranger is the fact that the order you declare the closures matters.

Test script:
---------------
<?php
/// TEST 1
///
/// Let's define two closures. Both 'use' $a by value.
///
$a = 123;
$fn1 = function () use ($a) { echo $a . "\n<br />"; };
$fn2 = function () use ($a) { echo $a . "\n<br />"; };

$a = 123;

$fn1 ();
$fn2 ();
//
// Analisys:
// 	In PHP 5.3.5 under Windows, outputs:
// 		123, 123
// 	Ok.
///
///
/// TEST 3
///
// Let's repeat TEST 1, but this time both closures 'use' $a by reference.
echo "---------------------------------------------------------\n<br />";
$a = 123;
$fn1 = function () use (&$a) { echo $a . "\n<br />"; };
$fn2 = function () use (&$a) { echo $a . "\n<br />"; };

$a = 456;

$fn1 ();
$fn2 ();
//
// Analisys:
// 	In PHP 5.3.5 under Windows, outputs:
// 		456, 456
// 	Ok.
///
///
/// TEST 3
///
/// Let's repeat TEST 1, but this time closure 1 'uses' $a by reference
/// closure 2 uses it by value.
///
echo "---------------------------------------------------------\n<br />";
$a = 123;
$fn1 = function () use (&$a) { echo $a . "\n<br />"; };
$fn2 = function () use ($a) { echo $a . "\n<br />"; };

$a = 456;

$fn1 ();
$fn2 ();
//
// Analisys:
// 	In PHP 5.3.5 under Windows, outputs:
// 		123, 123
// 	Wrong! It should output 456, 123.
///
///
/// TEST 4
///
/// Let's do same as in TEST 3 but now closure 1 'uses' by value and closure 2
/// 'uses' by reference.
///
echo "---------------------------------------------------------\n<br />";
$a = 123;
$fn1 = function () use ($a) { echo $a . "\n<br />"; };
$fn2 = function () use (&$a) { echo $a . "\n<br />"; };

$a = 456;

$fn1 ();
$fn2 ();
//
// Analisys:
// 	In PHP 5.3.5 under Windows, outputs:
// 		123, 456
// 	Ok. What the hell?


Expected result:
----------------
It should output:

123
123
---------------------------------------------------------
456
456
---------------------------------------------------------
456
123
---------------------------------------------------------
123
456 

Actual result:
--------------
Only Test 3 fails. The others are for helping finding the problem.


123
123
---------------------------------------------------------
456
456
---------------------------------------------------------
123
123
---------------------------------------------------------
123
456