To reproduce:

1. Download attached project "New Unity Project.zip" and open in Unity
2. Open "RagdollBug" scene
3. Open "Scene" and "Game" views
4. Press "Play" button
5. When Ragdoll falls press "Vanish" button
6. Press "Sight" button
Note: You will see that Ragdoll is laying on the ground
7. Focus on "Animator" window
8. Press "Vanish" button
9. Press "Sight" button

Expected result: After you pressed "Sight" button, you will see that Ragdoll is still laying on the ground
Actual result: After you pressed "Sight" button, you will see that Ragdoll starts falling again.

Note: If you delete disabled Animator component from "unitychan" game object, then this problem disapears and Ragdoll falls only once.

Reproduced on Unity 5.6.0f3, 2017.1.0b1,
Not Reproduced on Unity 5.5.3f1
Regression on Unity 5.6.0b9

Video is in "Game and Scene windows.webm" and "Delete Animator.webm"