I saw this bug "in action" and it's a weird one. When left to boot as usual, it says it can't find the network, although it's clear on the screen that it initialized it a bit earlier. But, if you boot with the "break=mount" boot parameter, it works like this: you get dropped to a shell after the network drivers are loaded, but before the NFS mount is attempted. All you have to do is press Control+D to continue, and then it boots just fine. It seems that the delay caused by dropping to that shell is enough for things to work. And it's always reproducible.