Find Usages does not find implementation of method for extended interface

Find Usages does not work for methods from extended interface.

Steps to reproduce:

1. Create interface "Generic"
2. Create interface "Special" extending "Generic"
3. Create class "SpecialImpl" implementing "Special" interface
4. Select method from "Generic" interface
5. Select Find Usages from context menu

Actual result: only method declaration in interface is found
Expected result: method implementation in class is found

Sample code:

namespace MyApp;

interface Generic {
    public function print();
}

interface Special extends Generic {
    public function printSpecial();
}

class SpecialImpl implements Special {
    public function print() {}
    public function printSpecial() {}
}