We are using snappy compression and noticed a fairly substantial increase (about 2.25x) in log filesystem space consumption after upgrading a Kafka cluster from 0.8.1.1 to 0.8.2.1. We found that this is caused by messages being seemingly recompressed individually (or possibly with a much smaller buffer or dictionary?) instead of as a batch as sent by producers. We eventually tracked down the change in compression ratio/scope to this  commit that updated the snappy version from 1.0.5 to 18.104.22.168. The Kafka client version does not appear to be relevant as we can reproduce this with both the 0.8.1.1 and 0.8.2.1 Producer.
Here are the log files from our troubleshooting that contain the same set of 1000 messages, for batch sizes of 1, 10, 100, and 1000. f9d9b was the last commit with 0.8.1.1-like behavior prior to f5ab8 introducing the issue.