Javac was not in sync with [JLS 8 §15.12.1](https://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.12.1), specifically:
 
If the form is TypeName . super . [TypeArguments] Identifier, then:
...
- Otherwise, TypeName denotes the interface to be searched, I.
 
Let T be the type declaration immediately enclosing the method invocation. It
is a compile-time error if I is not a direct superinterface of T, or if there exists some other direct superclass or direct superinterface of T, J, such that J is a subtype of I.

So javac was not issuing a compiler error for cases like:
```
interface I {
    default int f(){return 0;}
}
 
class J implements I {}
 
class T extends J implements I {
    public int f() {
        return I.super.f();
    }
}
```
The compiler had some checks for method invocations of the form:

`TypeName . super . [TypeArguments] Identifier`

but there was one issue. If `TypeName` is an interface `I` and `T` is the type declaration immediately enclosing the method invocation, the compiler must issue a compile-time error if there exists some other direct superclass or superinterface of `T`, let's call it `J` such that `J` is a subtype of `I`, as in the example above.