4.0.765.1 nightly repro steps: Create a new winforms app project Create a button Double click button to add handler enter: Person p = new Person(); press Alt+Enter for quick-fix create class Person press F6 on new class to move to another namespace (e.g. DomainModel) resharper moves class to top of file in new namespace. Ctrl+Tab to form designer gives the following error: The class Form1 can be designed, but is not the first class in the file. Visual Studio requires that designers use the first class in the file. Move the class code so that it is the first class in the file and try loading the designer again. In the code window, the partial class does not pick up that it has a second part. Probably the easiest way to fix this is by ensuring 'move to namespace' moves class to buttom of file, rather than the top.