I use a SimpleTest to do unit tests and it seems that it is this library which causes the memory leaks.

<?php
function simpleTestErrorHandler($severity, $message, $filename, $line) {
	restore_error_handler();
	TRUE; // Some PHP code
	set_error_handler('simpleTestErrorHandler');
}

class plip {

	public function run() {
		set_error_handler('simpleTestErrorHandler');
		trigger_error("plop", E_USER_NOTICE);
		restore_error_handler();
	}

}

$a = new plip;
for($i = 0; $i < 10000; $i++)
	$a->run();
?>

/usr/src/php5-200410111030/Zend/zend_builtin_functions.c(1058) :  Freeing 0x082D0C54 (16 bytes), script=/www/test2.php
Last leak repeated 9999 times
/usr/src/php5-200410111030/Zend/zend_variables.h(45) :  Freeing 0x082D0B84 (23 bytes), script=/www/test2.php
/usr/src/php5-200410111030/Zend/zend_variables.c(120) : Actual location (location was relayed)
Last leak repeated 9999 times

/Zend/zend_builtin_functions.c(1097) :  Freeing 0x08965664 (16 bytes), script=t.php
Last leak repeated 9999 times
/Zend/zend_variables.h(45) :  Freeing 0x08965594 (23 bytes), script=t.php
/Zend/zend_variables.c(120) : Actual location (location was relayed)
Last leak repeated 9999 times
=== Total 20000 memory leaks detected ===

/usr/src/php5-STABLE-200505070036/Zend/zend_builtin_functions.c(1090) :  Freeing 0x0824C56C (16 bytes), script=/www/test3.php
Last leak repeated 9999 times
/usr/src/php5-STABLE-200505070036/Zend/zend_builtin_functions.c(1100) :  Freeing 0x0824C49C (23 bytes), script=/www/test3.php
/usr/src/php5-STABLE-200505070036/Zend/zend_variables.c(137) : Actual location (location was relayed)
Last leak repeated 9999 times
=== Total 20000 memory leaks detected ===

This bug has been fixed in CVS.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
 
Thank you for the report, and for helping us make PHP better.