we need to have an option to turn off sending of diffs. There are a couple of really strong reasons I can think of to do this:
1) 3.3.x is broken in a similar way, there is an upgrade problem we can't solve short of having ppl first upgrade to a fixed 3.3 (3.3.5 say) and then upgrading to 3.4.x. If we could turn off diff sending this would address the problem.
2) safety valve. Say we find another new problem with diff sending in 3.4/3/5. Having an option to turn it off would be useful for people as a workaround until a fix is found and released.