Since 15w34a, if the player disconnects whilst having a chunk packet in their packet queue, the buffer (d) will never have .release() called on it, thus causing a memory leak.
MC-89805
Memory Leak When Player Disconnects Before Chunk Packet Sent
Resolved
Awaiting Response
4
Is this still an issue in the most recent versions (currently that is 1.10.2, or 16w42a) of Minecraft? If so, please update the affected versions and help us keeping this ticket updated from time to time.