PDF Embed API - right-hand panel missing after exit from fullscreen mode

Hi there,

I find that right-hand panel will be missing after exit from fullscreen mode. 

Steps to reproduce the issue:

1. Open the test site I made with PDF Embed API: https://share.dc1979.com/poc/

2. After the pdf preview loaded, click the fullscreen button on top-right corner to enter fullscreen mode

3. Press Esc to exit fullscreen mode

4. The right-hand panel (containing comments panel, page thumbnails, page navigation etc.) is missing, instead there is a broken panel shows in the bottom:

The preview config I used is: 

var viewerConfig = {
        embedMode: "FULL_WINDOW",
        defaultViewMode: "FIT_WIDTH",
        showDownloadPDF: false,
        showPrintPDF: false,
        showLeftHandPanel: false,
        showAnnotationTools: true,
        enableFormFilling: false,
        showDisabledSaveButton: false,
        showFullScreen: true,
        enableAnnotationAPIs: true,
        includePDFAnnotations: true,
};

So is this a bug, or am I missing something?

Thanks for any help.