Deepclone of same class with SubclassMapping

I'd like to use mapstruct to deepclone same objects. However situation is little bit trickier as I'm using abstraction.

public abstract class Fruit {

    private String id;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }
}

public class Banana extends Fruit {

    private String origin;

    public String getOrigin() {
        return origin;
    }

    public void setOrigin(String origin) {
        this.origin = origin;
    }
}

public class Apple extends Fruit {

    private String type;

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }
}

@Mapper(mappingControl = DeepClone.class, subclassExhaustiveStrategy = SubclassExhaustiveStrategy.RUNTIME_EXCEPTION)
public interface FruitMapper {


    @SubclassMapping(source = Apple.class, target = Apple.class)
    @SubclassMapping(source = Banana.class, target = Banana.class)
    Fruit clone(Fruit fruit);
}

and finally this is what is generated:

public class FruitMapperImpl implements FruitMapper {

    @Override
    public Fruit clone(Fruit fruit) {
        if ( fruit == null ) {
            return null;
        }

        if (fruit instanceof Apple) {
            return (Apple) fruit;
        }
        else if (fruit instanceof Banana) {
            return (Banana) fruit;
        }
        else {
            throw new IllegalArgumentException("Not all subclasses are supported for this mapping. Missing for " + fruit.getClass());
        }
    }
}

The thing I'm missing is the actual implementation of given subclasses. Is that a bug or is it designed like this? Because if I add method like Apple clone(Apple apple); then it should be good (for Apple only) however I don't see any benefit of adding SubclassMapping

public class FruitMapperImpl implements FruitMapper {

    @Override
    public Fruit clone(Fruit fruit) {
        if ( fruit == null ) {
            return null;
        }

        if (fruit instanceof Apple) {
            return clone( (Apple) fruit );
        }
        else if (fruit instanceof Banana) {
            return (Banana) fruit;
        }
        else {
            throw new IllegalArgumentException("Not all subclasses are supported for this mapping. Missing for " + fruit.getClass());
        }
    }

    @Override
    public Apple clone(Apple apple) {
        if ( apple == null ) {
            return null;
        }

        Apple apple1 = new Apple();

        apple1.setId( apple.getId() );
        apple1.setType( apple.getType() );

        return apple1;
    }
}

EDIT: issue created