Currently, when Mirror Maker 2 mirrors messages with headers, it will convert all headers from the original format into Base64 encoding using the default org.apache.kafka.connect.storage.SimpleHeaderConverter. This is not intended since it changes the mirrored messages. 

It should use the org.apache.kafka.connect.converters.ByteArrayConverter converter instead which keeps the headers intact. The same converter is already set as default for keys and values.