What causes partitions to be revoked?

[Scott Thibault]

I'm using the Kafka 1.0.1 Java client with 1 consumer and 1 partition and
using the ConsumerRebalanceListener I can see that the partition keeps
getting revoked and then reassigned.  My consumer is in it's own thread to
ensure poll is invoked regularly.  Is there some other reason this might be
happening?