1. Go to control panel,add a community,add a page to this community,and add Document Library to this page.
2. Add some files.
3. In Guest communtiy,also add Document Library portlet to a test page.
4. Add shortcut,select the newly created community,select files newly uploaded.
You would see the results as attached image.
But if you select the current community,it's working.
Otherwise,I tested it on 52x-64956,same steps,and no such issues.
So I assume it's a bug.