DESCRIPTION
Ok it seems that I mixed some files in the first upload, the thing is, the issues was that the rotation of the center bone could not be reliable be separated so that only the rotation in the y axis stayed in the center bone and the x and z would be passed on to the upper and lower body bones, this is why I recommend the center bone modification, any ways, the solution was just passing all rotation to the upper and lower body bones and leave movement only for the center bone, the results are the the same, for Izumi at least, as for other models, it should not be that big of a deal really.
The new download should be in your DM inbox by now.
Sorry for the inconvenience.