We use FileInfo to detect the type of file - that will have its own methods of detecting SVG.

What does this output on your server?

<?php

echo is_svg('/full/path/to/your/file.svg');

function is_svg($image_path) {

    if (function_exists('finfo_open')) {
        $finfo = finfo_open(FILEINFO_MIME_TYPE);
        if ($finfo) {
            $mime_type = finfo_file($finfo, $image_path);  
            finfo_close($finfo);

            if (strpos($mime_type, 'svg')) {
                return $mime_type;
            }
        } 
    }else{
        // This is deprecated, but throw me a bone
        if (function_exists('mime_content_type')) {
            $mime_type = mime_content_type($image_path);
            if ($mime_type && strpos($mime_type, 'svg')) {
                return $mime_type;
            }
        }
    }

    // This is not an exact science, people.
    if (isset($mime_type)) {
        if ($mime_type=='text/plain' && PerchUtil::file_extension($image_path)=='svg') {
            return 'image/svg+xml';
        }
        if ($mime_type=='text/plain' && PerchUtil::file_extension($image_path)=='svgz') {
            return 'image/svg+xml';
        }
    }

    return 'no clue';
}


?>

Is this on the production server?

Ok. I don't have a solution. It's something I'll need to see if we can accept for in the future.