fopen does not take include_path into consideration as of HipHop VM v2.1.0-dev. fopen's 3rd param when set to true should take all include paths into consideration when trying to open the file. http://php.net/manual/en/function.fopen.php

Folder Structure

A basic folder structure to replicate this is as follows:

./fopen.php
./someIncludeFolder/
./someIncludeFolder/someIncludedFile.php

fopen.php

<?php

$filename = 'someIncludedFile.php';

echo "Include path is: " . get_include_path() . "\n";

set_include_path(
    implode(
        PATH_SEPARATOR,
        array(
            './someIncludeFolder',
            get_include_path()
        )
    )
);

echo "Include path is now: " . get_include_path() . "\n";

if (!$fh = fopen($filename, 'r', true)) {

    echo "### INFO: Unable to open someIncludedFile.php\n";

} else {

    echo "### INFO: Opened someIncludedFile.php successfully\n";

}

OUTPUT

$ php fopen.php 
Include path is: .:/usr/share/php:/usr/share/pear
Include path is now: ./someIncludeFolder:.:/usr/share/php:/usr/share/pear
### INFO: Opened someIncludedFile.php successfully

$ hhvm fopen.php 
Include path is: ./
Include path is now: ./someIncludeFolder:./
HipHop Warning: No such file or directory in ./fopen.php on line 20
### INFO: Unable to open someIncludedFile.php

someIncludedFile.php

<?php

echo "This is someIncludedFile.php";