helperphp.php reverts back to original version

I've modified the file_manipulation/helperphp.php file at line 82 so that files are renamed properly, then converted to lowercase. All works fine for a while then the modified file reverts back to the original helperphp.php file without any intervention from me. How can I stop this happening?

I modified helperphp.php in the DW6 Configuration folder: Configuration\Shared\Webassist\DigitalFilePro\helpers\ on Windows 7
Now it's all fine. Must remember to change this when I update DataBridge.

Here's the extra code at line 81:

$baseFileName = preg_replace('/\.[^.]*$/', '', $uploadedFile["name"]);
$baseFileName = preg_replace('/[^A-Za-z0-9]/', '_', $baseFileName); // replaces all chrs & spaces except UC or LC letters & numbers with underscore
$baseFileName = preg_replace('/_+/', '_', $baseFileName); // Trims underscore: '___' >> '_'
$baseFileName = strtolower($baseFileName); //DGW makes lowercase

Cheers
Dave