Test:

---
import java.util.List;

public class GLBConflict {

    interface I<S> {}
    interface J<S> extends I<S> {}
    interface J2<S> extends I<S> {}
    interface K extends I<String> {}

    <T> T upper2(List<? super T> l1, List<? super T> l2) { return null; }

    void test(List<I<String>> i, List<J<Integer>> j, List<J2<String>> j2, List<K> k) {
        upper2(i, j); // expected: error; actual: error
        upper2(j, j2); // expected: error; actual: ok
        upper2(j, k); // expected: error; actual: ok
    }

}
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All three invocations of 'upper2' should fail, due to this clause (JLS 8 18.3):

"If two bounds have the form α <: S and α <: T, and if for some generic class or interface, G, there exists a supertype (4.10) of S of the form G<S1, ..., Sn> and a supertype of T of the form G<T1, ..., Tn>, then for all i, 1 ≤ i ≤ n, if Si and Ti are types (not wildcards), the constraint ⟨Si = Ti⟩ is implied."

Under '-source 7' and previous, there is not a clear specification for an error, but all three invocations otherwise produce a malformed intersection, which javac makes some effort to prevent. If the first one is an error (javac claims it is), the other two should be errors, too.