-Unable to move the red vertical bar in motion parameter diagram of Blend Tree. Value of the threshold parameter is changing but the red vertical bar stays at 0.
-Sometimes the red vertical bar is moving but its running ahead of the mouse cursor.

Steps to repro:
1. Create a new project > Create a Cube game object.
2. Windows > Animation > Animation > Click on Create button.
3. Project Window > Open Cube Animator > Create Blend Tree.
4. Open the Blend Tree > Right Click > Add > Add Motion.
5. Right Click > Add > Add Blend Tree.
6. Inspector > Select and Dragg red vertical bar.

Actual Result:
The red vertical bar is not moving in a motion parameter diagram.

Expected Result:
The red vertical bar should move in a motion parameter diagram.

Reproducible in:
2020.2.0a16, 2020.2.0a13.

Working fine in:
2020.2.0a12, 2020.1.0b14.

Environment:
Occurring on Windows 10 & Mac 10.15.