Root motion and transition custom blend logic

Hi everyone! I’m making root motion controller and can’t understand why my transition custom blend logic works in such unexpected way.

I made [simplified project][1], maybe someone can help.
I’m using three animations: Idle, Move and Jump. Move animation contains straight forward movement. Jump animation contains straight up movement.

Here is my Anim Graph:

202839-anim_graph.png

Under Red arrow you can find transition custom blend logic.

With standart blend logic i got expected result:

202840-standart_blend.png

In image above you can see where transition started (red sphere)

But when i use custom blend logic:

202841-custom_transition.png

I expects something like this:

202842-expected.png

However final result is absolutely similar to standart blend logic:

202843-custom_blend.png

Why i got this result and how i can fix this?

There is an answer to this, but it requires changing engine source:
https://forums.unrealengine.com/unreal-engine/feedback-for-epic/88174-separate-animation-blending-time-for-root-motion-from-the-actual-animation/page2