"Class String could not be loaded" PHP Haxe Error - php

Question

I'm getting the following stacktrace, which appears as if PHP chokes while attempting to parse the boot class:
<pre>uncaught exception: <b>Class String could not be loaded</b><br /><br />in file: /path/to/haxe-php-lib/lib/php/Boot.class.php line 751<br />#0 [internal function]: spl_autoload('String')
#1 /path/to/haxe-php-lib/lib/php/Boot.class.php(751): property_exists('String', '__meta__')
#2 /path/to/haxe-php-lib/lib/php/Boot.class.php(857): _hx_type->__construct('String', 'String')
#3 /path/to/NativePHPUtil.php(334): require_once('/path/to/haxe-php-lib/include.php') //include.php is basically `require_once dirname(__FILE__).'/lib/php/Boot.class.php'; restore_exception_handler();`
#4 [internal function]: NativePHPUtil->addRecord('record-name', 'record-type', Object(stdClass))
#5 /path/to/NativePHPController.php(244): call_user_func_array(Array, Array)
#6 /path/index.php(89): NativePHPController->handle()
#7 {main}</pre>
Function from Boot.class.php(751):
public function __construct($cn, $qn, $path = null) {
$this->__tname__ = $cn;
$this->__qname__ = $qn;
$this->__path__ = $path;
if(property_exists($cn, '__meta__'))
$this->__meta__ = eval($cn.'::$__meta__');
}
It doesn't appear to be getting to using haxe-php-lib, just loading the necessary files. So I tried turning off dead-code-removal for PHP and reverting to using the require_once dirname(__FILE__).'/lib/php/Boot.class.php' directly, no joy.
This just started happening on my testing server (PHP 5.3 on Debian) a few days ago and there were no obvious changes to prompt the issue. I've tried pulling down a fresh copy from Git and fiddling with permissions.
What is spl_autoload('String') doing? Any guesses as to what might be causing the issue?
Update We commented out the if statement and everything seems to be working just fine....