Crashes with Error Code 6 - Received passengers for unknown entity

Minecraft: Java has crashed several times over the last week with Error Code 6. The log files show a warning when loading chunks that says, "Received passengers for unknown entity."

I have attached the log files. The latest.log is when I am using OptiFine. The GZip file is when I am using Vanilla.

This world was originally created on a Linux Mint system and was ported to a Fedora system.