[1.8 FML] random concurrent access errors

So it's either FML or my environment(jre 1.8.0_20), but I've gotten this error in both source(client) and client releases. It doesn't always happen, there are times when I can load the world.

Client was installed with the launcher

Developers(source) version was run with the 1009 build, can update if need be

Client has had issues since initial install (build 1005) through to current build(1012).

Have tried clean installs on both sides-

No user mods included in the client build. Development environment has a core mod which does not have any effect on the issue.

Error Log from client

link

edit: sorry copied the wrong link! should be fixed now