Exactly. Relevant passage from ^

    An object is considered to be completely initialized when its constructor finishes. 
    A thread that can only see a reference to an object after that object has been completely 
    initialized is guaranteed to see the correctly initialized values for that object's final fields.

Thanks, that explains it! Didn't know that final fields have this special rule and that the value field in the String class is final.

So to recap: this shouldn't be possible for Strings, since the value field in the String class is final and therefore has a memory barrier. But it could happen for other classes with non-final fields.