C# script properties are not blended during animation transitions when clips are runtime changed on an OverrideController

To reproduce:

1. Download attached project "PlaygroundRepro.zip" and open in Unity
2. Open "Playground" Scene
3. Open the Playground control (Window->Playground Control)
4. Enter Play Mode
5. Click "Create Female Avatar"
6. Click on the eighth button along the top of the Playground Control window called "Animations" in the Playground control window (between Emotes and Precanned Avatars)
7. Select/Click on "Avatar 1" underneath the Create Male/Female Avatar buttons. A bunch of buttons with various names appear in the middle of the Playground Control window.
8. Click on the Cheer button (fourth from the bottom, in the rightmost column).

Expected Result: The avatar will play the Cheer animation, and then at the end, the legs do not float up and snap back down
Actual Result: The avatar will play the Cheer animation, and then at the end, the legs will start to float up before snapping back down. In Scene view (or on the Avatar 1 object in the hierarchy) you can see that the IK weighting is at 0 until the end of the transition, where it is suddenly set to 1, and the IK starts solving again. Instead, the IK weight values should blend between 0 and 1 during the animation transition.

Reproduced on Unity 5.6.1p4, 2017.1.0b10 and 2017.2.0a4