Thank you for this bug report. To properly diagnose the problem, we
need a short but complete example script to be able to reproduce
this bug ourselves. 

A proper reproducing script starts with <?php and ends with ?>,
is max. 10-20 lines long and does not require any external 
resources such as databases, etc. If the script requires a 
database to demonstrate the issue, please make sure it creates 
all necessary tables, stored procedures etc.

Please avoid embedding huge scripts into the report.

Okay, the full script with PHP tags:

<?php
function optimizeHTML( $html )
{
    $badwords_array = array(  );
    $replacement = '';
    
    $html = str_ireplace( $badwords_array, $replacement, $html );
    return $html;
}

ob_start( 'optimizeHTML' );
?>

This is CapItalized.

The I or C in CapItalized might be removed, as well as the T in This or The.

That's still incomplete, since it doesn't include the actual array you're giving str_ireplace() (which is kind of important).

Honestly, I'm kind of inclined to suspect it's a problem in your code, rather than PHP, since the following code works for me on PHP 5.2:

<?php
function filter_output($text) {
    $adjectives = array('quick', 'brown');
    return str_ireplace($adjectives, '', $text);
}

ob_start('filter_output');
echo 'The Quick Brown Fox Jumps Over The Lazy Dog';
ob_end_flush();

// Should end up printing "The   Fox Jumps Over The Lazy Dog"
?>

No feedback was provided. The bug is being suspended because
we assume that you are no longer experiencing the problem.
If this is not the case and you are able to provide the
information that was requested earlier, please do so and
change the status of the bug back to "Open". Thank you.