In our Intranet we got this nasty double encoding error that was introduced in SharePoint April 2014 CU. In July 2014 CU the problem is still there. I often hear the suggestions to update files directly in the hive (the root folder for SharePoint: C:\Program Files\Common Files\microsoft shared\Web Server Extensions\15\) In that blog post it is described what the problem is and what files are affected and what code must be altered in order to get it to work (which I like).