using @MappingTarget with @Default constructor annotated member class

Mapping method with @MappingTarget generates code that tries to alter immutable member instead of setting a new instance.

Example:
If I have a class with a constructor injected member:

public class DemonstratorTarget {
    private DemonstratorTargetEmbedded embedded;
    @Default
    public DemonstratorTarget(DemonstratorTargetEmbedded embedded) {        this.embedded = embedded;    }
    public DemonstratorTargetEmbedded getEmbedded() {        return embedded;    }
    public void setEmbedded(DemonstratorTargetEmbedded embedded) {        this.embedded = embedded;    }
}

with a supposedly immutable member class:

public class DemonstratorTargetEmbedded {
    private String version;
    private Map<String, String> metadata = new HashMap<>();
    public DemonstratorTargetEmbedded() {    }
    @Default
    public DemonstratorTargetEmbedded(String version, Map<String, String> metadata) {
        this.version = version;
        this.metadata = metadata;
    }
    public String getVersion() {        return version;    }
    public Map<String, String> getMetadata() {        return metadata;    }
}

and use it in a mapper as @MappingTarget:

@Mapper
public interface DemonstratorMapperBroken {
    void updateTarget(@MappingTarget DemonstratorTarget target, DemonstratorSource source);
}

The resulting mapper will not call target.setEmbedded([newly created instance]) but tries to alter the member:

            mappingTarget.getMetadata().clear();
            Map<String, String> map = demonstratorSourceEmbedded.getMetadata();
            if ( map != null ) {
                mappingTarget.getMetadata().putAll( map );
            }

This of course fails in the example above, because there is no setter for version.

Now if I change the mapper to look like this (added a mapping method, did not change the original one):

@Mapper
public interface DemonstratorMapperWorking {
    void updateTarget(@MappingTarget DemonstratorTarget target, DemonstratorSource source);
    DemonstratorTargetEmbedded toTargetEmbedded(DemonstratorSourceEmbedded gender);
}

...the mapper works as expected:

target.setEmbedded( toTargetEmbedded( source.getEmbedded() ) );
[...]
DemonstratorTargetEmbedded demonstratorTargetEmbedded = new DemonstratorTargetEmbedded( version, metadata );

I am unsure if this is expected behaviour. Is there a way to circumvent this without adding a method like toTargetEmbedded?

I created a demonstrator:

1. git clone -b mapstruct-constructor-mapping https://github.com/mickroll/demonstrator.git
2. cd demonstrator
3. mvn clean install