The mean preserving spread is defined as follows:
Consider two lotteries g and h. Let $x_g$ und $x_h$ denote the corresponding random variables. Then h is a mean preserving spread (MPS) of g, if: $x_h = x_g + z$ for some random variable z with $E[z|x_g] = 0\ \forall\ x_g$. (This definition is supposed to be complete and exhaustive and I have found it in multiple sources)
My problem is: As far as I understand it, g (the old lottery) is also a mean preserving spread of h (the new lottery). At least the definition from the beginning allows for this: If I set z in a manner that the first outcome becomes larger and the second one smaller, I can still have $E[z|x_g] = 0\ \forall\ x_g$, but the total risk is now smaller. I have basically spread the lottery negatively. Just that MPS is now an entirely useless concept, since it does not allow for judgements with regards to the value of utility for an individual with concave utility functions (or any other shape for that matter.