After applying the July 2014 CU for SharePoint server, I discovered that Person or Group (People Picker) fields are not populated with server values in list item Edit forms. However, the field values can be viewed in list views and in Display forms. I examined the client side code and determined that field data is not being returned from the server for Edit forms.
In a test environment, I uninstalled SharePoint 2013, reinstalled SP 2013 with SP1 and the issue went away. I then applied the May 2014, June 2014, and July 2014 CUs. The issue did not exist after applying the May and June CUs. It did exist after applying the July 2014 CU.