Steps to reproduce:
1. Open the provided project "Foot IK Timeline preview.zip"
2. Select the "New Timeline" GameObject in the Hierarchy window
3. In the Timeline window select "New animation" Animation track
4. Press play to preview the animation
5. In the Inspector window check and uncheck Foot IK property while the animation is running

Expected results: Foot IK property affects the animation
Actual results: Foot IK property does not affect the animation when Timeline preview is played

Reproducible with: Timeline 1.1.0 (2019.3.0a8), Timeline 1.2.6 (2019.3.0b11), Timeline 1.3.0 (2020.1.0a13)
Not reproducible with: Timeline 1.1.0 (2019.2.13f1),Timeline 1.1.0 (2019.3.0a7)

Note: While in Play Mode, Foot IK property affects the animation