Repro steps:

1. Open "AnimationBug" project
2. Enter Play mode
3. Look at the animation transitions

Expected result: The animations should go as the user defined
Actual result: One of the animations pops in for a frame while transitioning between animations

Reproduced with: 2017.2.0a3, 2017.1.0b9, 5.6.1p4, 5.6.1p1, 5.6.0f3, 5.5.4f1,
Did not reproduce on: 5.4.5p3 (Project doesn't work/crashes)

Fixed on: 2017.3.0a5

Note:
The animation transitions are changed in the "AnimatorTest.cs" script
The bug only happens when the animation change is instant,but if you call "WaitForSeconds" it goes as expected
A "workaround" is to change line 90 to "yield return new WaitForSeconds(0.8f * Time.timeScale);"