A typed list as return type in an abstract method returns a list of objects - why?

Question

I'm confused - and need help. I've an abstract class with an abstract method:

public abstract class AbstractA<T extends SomeOtherClass> {

    public abstract List<String> getAll();

}

When I declare a method parameter of type AbstractA and call getAll() the IDE shows me the correct return type (List<String>).

...

public void test(AbstractA abstractA) {
    abstractA.getAll(); // <- returns List<String>
}

...

But when I want to iterate over that list, each element is of type Object and not String:

...

public void test(AbstractA abstractA) {
    for(String element : abstractA.getAll()) {  // <- compile error: 
     // error: incompatible types: Object cannot be converted to String
    }
}

...

And it gets even better:

...

public void test(AbstractA abstractA) {
    List<String> myElements = abstractA.getAll();
    for(String element : myElements) { // <- this is correct!
    }
}

...

I've no idea what's going on here. I'am using Java 8 (update 25). Can anyone explain to me why the compiler did not accept an iteration over my list?

I really appreciate your help.

Best regards, Daniel