Steps to reproduce:

1. Open attached project "Flicker.zip"
2. Open scene "Main"
3. In hierarchy, select "Camera/Canvas/Panel/BtnTest"
4. In its Animator, click on Controller field and notice that it uses Override controller
5. Run scene
6. Spam-click "Open Interface" button which is visible in scene
7. Notice that for a split of a second button turns orange. That is its default state and this behavior isn't expected
8. Stop the scene and in hierarchy, select "Camera/Canvas/Panel/BtnTest"
9. Change its animator controller to "_BtnDefaultController"
10. Run scene again and click on "Open Interface" once
11. Notice that button flickers
12. Now spam-click on "Open Interface" and notice that button no longer flickers

Conclusion:
1. Using Animator Override Controller causes default state to be displayed for a frame each time animation is played
2. Using (normal) Animator Controller makes default state to be displayed only once - first time animation is played

Regression introduced in 5.2.1p3
Reproduced with: 5.3.0f4, 5.4.0a5