generics: problem with equivalence of generic types

The following program fails to compile using the generics compiler:

/*
 * @test %W% %E%
 * @bug 4738171
 * @summary generics: problem with equivalence of generic types
 * @author gafter
 *
 * @compile/fail -source 1.5 T4738171.java
 */

interface If<T> {
    final If<T> C0 = null;
}

class Cl1<T> implements If<T> {
    final If<T> C1 = null;
    If<T> f1() {
        If<T> c1 = C0; // incompatible types found: If<T> required: If<T>
        If<T> c2 = C1;
        return C0; // incompatible types found: If<T> required: If<T>
    }
}

class Cl2<T> extends Cl1<T> {
    final If<T> C2 = new Cl2<T>();
    // non-static class T cannot be referenced from a static context
    // but why can class T be referenced in the type declaration ?
    If<T> f2() {
        If<T> c1 = C0; // incompatible types found: If<T> required: If<T>
        If<T> c2 = C2;
        return C1; // incompatible types found: If<T> required: If<T>
    }
}