Why “t instanceof T” is not allowed where T is a type parameter and t is a variable?

Question

Eclipse says that the instanceof operation is not allowed with Type Parameter due to generic type eraser.

I agree that at runtime, no type information stays. But con

Answer 1

After compiling statement o instanceof T would be o instanceof Object and because all types derives from Object, it will always evaluate to true. Allowing this kind of tests would give false positive results