PHPPresentation - issue loading then saving PP07 file

Question

I'm having issues just loading a PowerPoint 2007 (.pptx) file then saving it again. Even without making any changes to it the images from the original file end up missing.

    require_once 'PHPPresentation-develop/src/PhpPresentation/Autoloader.php';
    \PhpOffice\PhpPresentation\Autoloader::register();
    require_once 'Common-0.2.6/src/Common/Autoloader.php';
    \PhpOffice\Common\Autoloader::register();

    use PhpOffice\PhpPresentation\Autoloader;
    use PhpOffice\PhpPresentation\Settings;
    use PhpOffice\PhpPresentation\IOFactory;
    use PhpOffice\PhpPresentation\Slide;
    use PhpOffice\PhpPresentation\Slide\SlideLayout ;
    use PhpOffice\PhpPresentation\PhpPresentation;
    use PhpOffice\PhpPresentation\AbstractShape;
    use PhpOffice\PhpPresentation\DocumentLayout;
    use PhpOffice\PhpPresentation\Shape\Drawing;
    use PhpOffice\PhpPresentation\Shape\RichText;
    use PhpOffice\PhpPresentation\Shape\RichText\BreakElement;
    use PhpOffice\PhpPresentation\Shape\RichText\TextElement;
    use PhpOffice\PhpPresentation\Shape\Media;
    use PhpOffice\PhpPresentation\Style\Alignment;
    use PhpOffice\PhpPresentation\Style\Bullet;
    use PhpOffice\PhpPresentation\Style\Color;
    error_reporting(E_ALL);

    $oReader = IOFactory::createReader('PowerPoint2007');
    $readPPTX = $oReader->load(__DIR__ . '/input.pptx');
    $oWriterPPTX = IOFactory::createWriter($readPPTX, 'PowerPoint2007');
    $oWriterPPTX->save(__DIR__ . "/output.pptx");

In this snippet for example after I execute it, the output file is only 25321 bytes compared to the original which is 109363 bytes long - due to the images.

No errors are generated. I've tried it with both the develop and 0.7.0 branches.

Any ideas?