Offsets in Kafka producer start with -1 for new topic

[Thakrar, Jayesh]

I created a new Kafka topic with 1 partition and then sent 10 messages using 
the KafkaProducer API using the async callback.
What I saw was that the offsets in the RecordMetadata for the first record was 
-1.
Shouldn't it be 0 as offsets start with 0?

Is it a bug or works as expected?

Thanks,
Jayesh