The type system should give guarantees. I believe these cases violate the specification, and I think the specification is right to require the typechecker to check all code rather than just most code: a type system that works 100% of the time is much more useful than a type system that works 99.99% of the time, because it means you can blindly rely on it rather than having to double-check it every time you do anything critical and then maintain all those double-checks.

If we take the view that these are bugs in the Java compiler, then of course a bug that's rarely triggered is less bad than a bug that's triggered all the time. But both are bugs all the same.