I took another look at the bug and found out it's more a reflectionProperty bug:

-- File 'A.class.php'
<?PHP
class A{	
}
?>

-- File test.php in the same directory
<?php
/** autoload functie voor PHP5 */
function __autoload($classname) {
	if(file_exists("$classname.class.php"))
		include("$classname.class.php");
}
//When you include the following line, it works
//include("A.class.php");

class B{
	public function doit(A $a){
	}
}

$ref = new reflectionMethod('B','doit');
$parameters = $ref->getParameters();	
foreach($parameters as $parameter){
	//the following line give the error
	$class = $parameter->getClass();	
	echo $class->name;
}
?>

--Expected result
'A'

-- Actual result
Fatal error: Uncaught exception 'ReflectionException' with message 'Class A does not exist'

A possible solution might be to also check if zend_fetch_class() also returns null, next to zend_hash_find().

I'm not able to compile it myself, but the fix might be to change line 1703 in zend_reflection_api.c from
		if (zend_hash_find(EG(class_table), lcname, param->arg_info->class_name_len + 1, (void **) &pce) == FAILURE) {

to

		if (zend_hash_find(EG(class_table), lcname, param->arg_info->class_name_len + 1, (void **) &pce) == FAILURE
			&& zend_fetch_class(lcname, (param->arg_info->class_name_len + 1), ZEND_FETCH_CLASS_AUTO TSRMLS_CC) == NULL) {

Please try using this CVS snapshot:

  http://snaps.php.net/php5-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php5-win32-latest.zip

No feedback was provided for this bug for over a week, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".

I still encounter this bug in PHP 5.1.0RC1 on Win2k, also in  snapshot from Oct 12, 2005 02:30 GMT.
Here's a shorter reproduce code:

function foo(Bar $bar) {}

function __autoload($c) {
	class bar {}
}

$RF = new ReflectionFunction('foo');
foreach($RF->getParameters() as $param) {
	var_dump($param->getClass());
}

Still not fixed. tested with latest CVS

Fixed in CVS HEAD and PHP_5_1.