So I created a minimal working example where this behaviour can still be seen. It is 15 LOC and can be downloaded here: https://github.com/JonasGroeger/flink-inetaddress-zeroed
To run it, use sbt: If you don't want to do the above fear not, here is the code: For some reason, java.net.InetAddress objects get zeroed. Why is that? -- View this message in context: http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/keyBy-called-twice-Second-time-INetAddress-and-Array-Byte-are-empty-tp10907p10947.html Sent from the Apache Flink User Mailing List archive. mailing list archive at Nabble.com.