What O Sensei called tai no henka is what we call a pivot.
Tai no henka is not a 180° backward rotation around uke by means of a large step. This view is the result of a misunderstanding, and it must be corrected.
Tai no henka is a 270° pivot without taking a step. This is what throws uke off balance.
There is no other possible way to pivot 270° than by shifting your weight onto the heel of your front foot from the second third of the rotation onwards. The video demonstrates this:
There is no step because a pivot is a rotation around an axis; it is not a displacement in space.
The step, whether forwards or backwards, occurs only after tai no henka, as an effect of the pivot, as its consequence.
