Description:
------------
preg_replace blanks a string that it didn't use to in previous versions of PHP 5.x. other preg_replace strings not affected


Reproduce code:
---------------
function doSmiles($string, $skinname)
	{
	$patterns = array(
		"/\[alien\]/i",
		... snipped due to length ...
		"/\[crazy\]/i"
		);
	$replacements = array(
		"<img src=\"./skin/$skinname/emotes/alien.png\" alt=\"alien\" title=\"alien\">",
		... snip due to length ...
		"<img src=\"./skin/$skinname/emotes/crazy.png\" src=\"./skin/$skinname/emotes/crazy.png\" alt=\"crazy\" title=\"crazy\">"
		);

	$string = preg_replace($patterns, $replacements, $string);
	return $string;
	}


Expected result:
----------------
print substrings like [alien] to html-valid strings like <img src="./skin/default/alien.png">. prior to upgrading to 5.2.5 this particular function DID work. it no longer works.

Actual result:
--------------
returns a blank string ""