PHP+GD creating random black thumbnails

Question

Hello, This function is creating some random black images like.. 10% of the time, is not much, but.. you know.. shouldnt be happening.

class ImgResizer {
private $originalFile = '';
public function __construct($originalFile = '') {
    $this -> originalFile = $originalFile;
}
public function resize($newWidth, $targetFile) {
    if (empty($newWidth) || empty($targetFile)) {
        return false;
    }
    $src = imagecreatefromjpeg($this -> originalFile);
    list($width, $height) = getimagesize($this -> originalFile);
    $newHeight = ($height / $width) * $newWidth;

    if ($newHeight<'335') {
        //$newHeight='335';
    }
    $tmp = imagecreatetruecolor($newWidth, $newHeight);
    #$tmp = imagecreate($newWidth, $newHeight);
    imagecopyresampled($tmp, $src, 0, 0, 0, 0, $newWidth, $newHeight, $width, $height);
    if (file_exists($targetFile)) {
        unlink($targetFile);
    }
    imagejpeg($tmp, $targetFile, 85); // 85 is my choice, make it between 0 – 100 for output image quality with 100 being the most luxurious
}

}

no errors given in error_log. Here is gd_info():

Array(
[GD Version] => bundled (2.0.34 compatible)
[FreeType Support] => 
[T1Lib Support] => 
[GIF Read Support] => 1
[GIF Create Support] => 1
[JPG Support] => 1
[PNG Support] => 1
[WBMP Support] => 1
[XPM Support] => 1
[XBM Support] => 1
[JIS-mapped Japanese Font Support] => )1

server is linux. function is being called like this: assuming $imagen is the actual source image, and $imagendestino is the path and filename of the new thumbnail.

if (!file_exists($imagendestino)) {
        $work = new ImgResizer($imagen);
        $work -> resize(475, $imagendestino);
    }

Thanks in advance!