While blending an animation clip and timeline, only the animation clip is played if timeline is in the second order. Everything works vise versa.

To reproduce:
1. Open users attached project "TimelineMixingBug.zip"
2. Enter play mode and select Sphere game object from the hierarchy
3. Observe as the sphere is hovering up and down
4. In the Spheres components > Mixing Timeline Bug Example_README adjust the weight value from 0 to 1
5. Observe as the Sphere stops hovering and does nothing
6. Adjust the weight value from 1 to 0 and enable Timeline First setting in the same component
7. Observe as the Sphere starts to scale up and down
8. While Timeline first is enabled you can adjust the weight from 0 to 1 and see that the sphere is always animated
9. In the Window > PlayableGraph Visualizer in the top left select Sphere(Anim Controller)
10. Observe how the order of the animations changes while enabling or disabling Timeline First option

Expected result: animation and timeline always blends without problems
Actual result: if timeline is in the second order only the animation clip plays

Reproduced on:2017.1.0b10 2017.1.0f1 2017.1.0p4 217.2.0f2 2017.3.0b2

Notes: could not test for regression since the timeline came in 2017.1.0b1