Suppose I have two interfaces :

public interface Mother {}
public interface Son extends Mother {}

If I do "Move Class" from Son interface and select Mother in "To Type" option, I have the following result :

public interface Mother {
      public static class Son implements Mother {}
}

What I expected was : 

public interface Mother {
    public interface Son extends Mother {}
}

Regards.

FYI : it works for "to package" option.