From what I can tell, he's doing a big code rework for optimization purposes. That's probably partially on me, as I gave him a pretty decent amount of advice on how to go about that. Adding on to his own optimization efforts (Which probably account for much more than my advice), and if he received additional help, I assume that's where the delays/bugs are coming from.
Still, if it was going to cause this much delay, he should have notified people.