Error in json response when uploading file

In the administration backend, when adding a file to attribute of type object relations, the file upload will fail and the following error will be displayed: "Unable to parse the JSON response."

The issue seems to affect Internet Explorer only.

Steps to reproduce:

Start with a content class with an attribute of type object relations.

1. Create a new content object
2. Click the "Upload a file" button
3. Browse your filesystem and select a file to upload
4. Click the "Upload the file" button

You will get the following error (see attached screenshot):

Unable to parse the JSON response.