Repository Access Management not working in IE8

When opening the repository 'access management' tab in Internet Explorer 8, the user list is not loaded. The message "Loading..." is displayed, but nothing happens. It is also not possible to add users with read, write or admin access. When entering the user name manually, BitBucket shows an error message "No user named ...", although a user with this name definitely exists. This also happens when selecting a ame from the search-as-you-type list that appears when manually entering a user name.

Everything works fine in Safari (Mobile), so I guess it is a browser issue.