It could also mean Skarlet's u3 puts her in a neutral jump state (just u), while Kitana's b2 is a generic jump state (all of ub/uf/u) while Mileena's u4 never puts her in a jump states at all, you're just inputting up.
Changing Skarlet's u3 from a nj state into a generic jump state like kitana's b2 would fix the bug.
It's just theory, I also think it's probably not supposed to be that way.
you can cancel the slide directly into an upslash or downslash. probably a side effect of being able to cancel the dash into the slashes.