Description:
------------
<?php
ob_start();
echo "Hello world";
echo $a; 
ob_end_clean();
?>

Output:
PHP Notice:  Undefined variable: a in /home/karthik/scripts/a1.php on line 4
PHP Stack trace:
PHP   1. {main}() /home/karthik/scripts/a1.php:0

Here, even notice shouldn't have been there in the output. Does notices bypass this buffer?
If the same script is run through browser, the output is empty as expected.

Test script:
---------------
<?php
ob_start();
echo "Hello world";
echo $a; 
ob_end_clean();
?>


Expected result:
----------------
The output should be empty.

Actual result:
--------------
PHP Notice:  Undefined variable: a in /home/karthik/scripts/a1.php on line 4
PHP Stack trace:
PHP   1. {main}() /home/karthik/scripts/a1.php:0