For some strange reason when my existing projects referenced Type Mock and Type Mock Isolator it would mark Type Mock as copy local true and Isolator as false. However, after upgrading to 5.3.4 when I add a reference the opposite occurs. This causes a problem when upgrading a project and the project continues to use Type Mock as the local copy (5.3.1) and Isolator and the new version (5.3.4). This leads to some strange behaviour. So double check your references after upgrading.