re: Stage 2 engines
The strangest upper stage ignition I've heard of is Soyuz - when the upper stage engines ignite BEFORE seperation (hence the lattice interstage framework) - pity they've never done the whole rocket-cam effort onboard Soyuz.
The RL-10 nozzle is huge - and it wobbles around a hell of a lot under power.
The sep springs for this Falcon launch must have been a little asymetrical perhaps, as I've never seen a seperation go off-angle like that before.
Doug