How to reproduce:
1. Download and open attached "Transition" project
2. Open Scene "Transition" and select "timeline1" object
3. Click Pause and enter Play Mode
4. Click Step to next frame until the end of "up" animation in "timeline1"
5. Click Step several times more to observe the issue

Expected result: Cube object finishes animation in Timeline and goes back to "left" animation state in Animator
Actual result: Cube object finishes animation in Timeline, gets stuck and does not go back to "left" animation state in Animator

Reproduces with: 2017.3.0a1, 2017.4.8f1, 2018.1.9f1, 2018.2.1f1, 2018.3.0a6
Does not reproduce with: 2017.1.5f1, 2017.2.3p2

Notes: Simply entering Play Mode does what is expected.