MDSFailover: Master page mismatch – SOLVED!

One of the promising new features in SharePoint 2013 is the Minimal Download Strategy, which allows pages in non-publishing sites to be rendered using AJAX callbacks rather than full round trips and page refreshes. When it works, it provides a very seamless user experience, with only the essential portions of the page being changed.

However, when MDS fails, there is not much to go on.