The Find Usages feature fails to find a method
usage through supertype (interface) declared as
nested in a separate file. 
Consider the following example

A.java ---------------

public class A implements Main.Ints { 
    public int ten() { return 10;}          
}

Main.java ------------

public class Main {  
    interface Ints { 
        int ten() ;
    }
    
    public static void main(String[] args) {
        Ints ints = new A();
        System.out.print(ints.ten());
    }
}


Now, when searching of usage of A.ten(), nothing
is returned or just the definiton itself, when
"Find overriding methods" is clicked.

When class A was defined in Main.java (i.e. the
same file as the usage), or A was separate and
interface Ints was also in a separate file, not
nested, the usage was found correctly. 
It doesn't work when the supertype is nested and
the subtype is in a different file (nested or not).
 
I set it as P2 as such a bug disqualifies the
whole feature. When I encountered it, I had quite
a long hard time figuring out how could the
program work if the method was never called. Then
I returned to grep and I'm happy :-)