So I jumped out 100,000 blocks and generated this error in my console.

https://gist.github.com/anonymous/142e5f17a79dcdfa88cc4f0b4d3b3523

Official crash report of the above

https://gist.github.com/4a1b69b1e748ae417c31337572515a9e

Is this being caused by farseek, it's the last mod I see in the stack trace?

This error is a symptom of an infinite loop (see MinecraftForge/FML#483) but it's not clear whether it's mainly caused by Farseek/Streams or another mod. I'll investigate.