[Siegmund]

I think it's confusion over what is meant by "one hand." If you split a pair, you now choose what action to take on each half and have two outcomes you add together. If you count a split as 'two hands' you have a situation where the number of hands you play per initial bet depends on your strategy, and you might make additional bets before you are done acting on your hand.

But I think the common usage is that when we calculate the EV and SD per initial bet, we count the complete series of events that follows including splits and doubles and insurance as "one hand" despite the fact that more chips might be committed beyond the initial bet.