Animation depends on building a "skeleton" that pulls on the "skin" of the character to a greater or lesser degree ("weighting"), e.g. the "bone" in the upper arm mostly affects the skin on the upper arm, but it also has some effect on the flesh of the upper body.
In this, the weighting values for the Zangief/Sakura's skull are still set to work on Zangief's much more weirdly-shaped head.