The author @pixlepix not sure what happened so he sent me here. Unfortunately I was unable to reproduce it since that (tried other generators and RF storage blocks as well).

http://hastebin.com/egaviwawac.vhdl

I have no idea what happened to cause this. I'm going to have to say this is a race condition that exists in mojang's code, unless someone can reliably reproduce this.

Worth noting that, as far as I can tell, this doesn't have much to do with my code. My code mentioned in the stacktrace just updates neighboring blocks.