Chooser "Unable to Communicate With Parent Window" When Website Run as iOS Desktop Shortcut

I have a website I am developing which includes dropbox "chooser" functionality. Everything was working great in all of my testing so far, but when I created a shortcut to the website on the iOS desktop, dropbox chooser broke. The behavior I'm seeing now is when I click the button which invokes chooser, I immediately see the "unable to communicate with parent window" message at the login screen. It allows me to log in and navigate to the file I wish to select, but when I actually try to select it, I again see the "unable to communicate with parent window" message, and I'm unable to continue.

Because the dropbox functionality works fine when the website is viewed in the "normal" Safari browser, but not when Safari is launched via the iOS desktop shortcut, I'm thinking this is an issue which you need to look into, rather than something I messed up on my end. Here's the code I have in my web page, which is pretty vanilla:

<script type="text/javascript" src="https://www.dropbox.com/static/api/2/dropins.js" id="dropboxjs" data-app-key="MYKEYHERE"></script>

On my button I have the following:

function startDropboxProcess() {
  Dropbox.choose({
    success: function(files) {
      // Do something with the returned file
    },
     cancel: function() {
      hidePleaseWait();
    },
     linkType: "direct",
     multiselect: false,
     extensions: ['.pdf'],
  });
}

The iPad tells me it is running iOS 8.3. I can't seem to find what version of Safari it's using.